CHAPTER 1 Microprocessors and Binary Numbers
CHAPTER 2 Contructional Notes
CHAPTER 3 The Microtan 65
CHAPTER 4 The Microtan System
CHAPTER 5 The 6502 Microprocessor. Tables of Machine Instructions.
CHAPTER 6 Using TANBUG. Tables of Hex ASCII Codes. TANBUG Listing.
CHAPTER 7 Some Games Programs.
Unlike most other microcomputers, microtan 65 has been designed from
the start with a small system in mind, therefore expansion of microtan
65 is a concept, not an after thought. We hope that this manual will be
the first of many, as each Tangerine product is supplied with thorough
and useful documentation, an absolute necessity with anything related to
computers. The first chapter of this manual provides an introduction to
microprocessors and the binary number system, it is by no means complete
as this subject requires a complete book to be dedicated to it. Chapter
two gives contructional notes for the kit version but purchasers of ready
built microtan 65's are still advised to read it as it contains relevant
information. Chapters three and four describe the microtan 65 and the microtan
system respectively. The 6502 microprocessor is described in sufficient
detail in chapter five which also contains complete tables of all of the
6502 machine code instructions.
TANBUG, the most important item, is fully described in chapter six with a step by step guide and an example program to demonstrate the power of TANBUG's debugging aids. Also given in chapter six is a table of hex ASCII codes and the complete TANBUG listing. Games programs have been provided in chapter seven.
A fully expanded microtan 65 contains the 6502 microprocessor, 1K rom containing TANBUG, 1K RAM which is used for display memory and user program, keyboard interface, VDU logic and tri-state address buffers. The basic block diagram of the microtan 65 is shown below.
The most important aspect of the design is that the address multiplexer is switching at the processor clock rate. This can be done with the 6502 as memory accesses will only occur on one phase of the clock i.e. when 02 is high. WHen 02 is low the memory is not selected. During this time the VDU logic reads the display memory, one location at a time and decodes memory contents as alphanumeric or graphics characters. You will also notice when using microtan 65 that the display is free from annoying speckles, spots and flashes. This is because there is no conflict of access to display memory between processor and display refresh logic. In fact you can run a program that actually resides in display memory and it will run at full speed without upsetting the display ! The address and data bus timing is shown below to illustrate this.
Memory mapped display: Pages 2 and 3 of the address space (see chapter on the 6502) are used as the display memory, that is from hex location 200 to hex 3FF. Location 200 is the top left hand corner character position. Location 201 is the second character position in the top row and so on. The diagram below illustrates this more clearly.
To write a particular character into a character cell in the display the user must write the ASCII code, or whatever, for that character in the correct memory location. For example, if it was required to write the character "W" in the bottom row third column then the ASCII code 57 (for W) should be placed in memory loaction 3E2. If you use TANBUG's memory modify command M to load characters into the display remember that the display scrolls automatically and the character may be output onto a different row than intended.
Memory mapping of the microtan 65 is controlled on-board by three wire links, when used without the TANEX exapansion board. As there is only 1K RAM, 1K ROM and 6 I/O locations on the microtan 65 each of the three are allowed to repeat through defined areas of the 64K address space to simplify design. The address map is represented diagramatically below.
As can be seen the address space is divided into only three blocks and therefore only two bits of the address bus are necessary to control this map. The two bits used for memory mapping are the most significant address bits A15 and A14. Three links are used to wire in this address map on the microtan 65. When TANEX is used however, all memory mapping is controlled on the TANEX board and not on the microtan 65. To modify the microtan 65 it is only necessary to cut these three links.
RAM and ROM hardware is of really no consequence to the user but a knowledge
of the on-board I/O ports is useful. There are six peripheral ports used
on the microtan 65 cpu board and these control graphics on and off, keyboard
read and write, keyboard interrupt flag clear and delayed non-maskable
interrupt (used for single instruction and breakpoints). Each one of these
will be taken in turn:
a) Graphics on and off: The display refresh controller reads the display memory a byte at a time and interprets the bottom seven bits of each byte to be an ASCII coded character. There is however a ninth bit which can only be written to by the cpu. This ninth bit comes from the 2102 1K x 1 bit RAM chip in the graphics option. If at a certain display location the ninth bit, or graphics bit, is a logic one the data byte read is not decoded as an ASCII character but is instead used to build up a graphics block of 2 x 4 pixels, in the character cell position.
The graphics on and graphics off I/O ports control an R-S flip-flop, the output of which is the data input to the 2102 RAM chip. Therefore if the graphics flip-flop is in the on position each character written to the display memory will be decoded as a graphics character. Because the cpu cannot read the graphics bit directly it is not possible to scroll displays containing graphics. As displays containing graphics are rarely scrolled anyway this should not prove to be too much of a handicap.
The operations required to write graphics characters to the display is to firstly turn the graphics on by executing the assembly code instruction LDA BFF0. Each character then written to display will be a graphics character until graphics are turned off by executing the assembly code instruction STA BFF3.
b) Keyboard read, write and interrupt clear: There is both an input and output port on the keyboard socket. The output port is used only for strobing the 20 key keypad. This output port is used by executing the assembly code instruction STA BFF2. The input port is used for both types of keyboard. When using the alphanumeric keyboard the strobe from the keyboard is used to clock a flip-flop (the keyboard interrupt flip-flop). The output of this flip-flop is the keyboard interrupt flag and forms the eight input bit to the keyboard input port. If interrupts are enabled in the cpu then an interrupt will be generated by the keyboard strobe. Reading the keayboard input port will then allow the cpu to test whether or not the interrupt was generated by the keyboard or some other device. If interrupts are not enabled then the keyboard interrupt flag will still be set but will not generate an interrupt. It is possible to read the flag by reading the keyboard interrupt port, thus a strobe from an alphanumeric keyboard can be detected either by an interrupt or by software polling. Which ever technique is used though it will be necessary to reset the keyboard interrupt flag after is has been set and detected in order that is its ready to register a further keyboard strobe. To reset the keyboard interrupt flag the assembly instruction STA BFF0 should be executed. The keyboard port is read by the instruction LDA BFF3.
c) Delayed non-maskable interrupt: This facility is used by the monitor program TANBUG when executing single instructions and breakpoints. It should not be used in a used program. Users who will contemplate using the non-maskable interrupt in special applications will probably not be using TANBUG. In these cases the link LKNMI should be broken and the non-maskable interrupt may be driven via the board connector.
The TANBUG monitor program is located in 1K bytes of read only memory (ROM) at the top of the address space i.e. pages 252-255. It contains facilities to enter, modify, run and debug programs. This chapter of the manual gives full details of the command facilities and subroutines available to the user.
TANBUG will only operate in the memory map of the microtan system, it
is not a general purpose 6502 software and has been specifically written
for microtan. Locations F7F7, F7F8 and F7F9 are reserved for a jump to
an expansion monitor ROM which is positioned on the expansion board, more
about this later.
Locations 200-3FF i.e. pages 2 and 3 are the visual display memory -TANBUG writes to these locations whenever a command is typed to the monitor. Locations 100-1FF i.e. page 1, are used as the stack by the microprocessor. Since the stack is of the push down variety it follows that the whole of the page will not be used as stack storage in the majority of programs. TANBUG requires to use locations 1F0-1FF as stack storage (only 16 locations). The rest of this area is free for user programs. Locations 40-FF are also available as user RAM, the preceeding locations 0-3F being reserved for use by TANBUG. User programs which do not use the stack may therefore be loaded anywhere i.e. the area 40-1EF. For user programs which do use the stack, the user must calculate how many stack locations are required and reduce the upper limit accordingly.
TANBUG conatins coding to automatically identify whether the keypad or full ASCII keyboard is connected to the keyboard socket. This coding is executed every time a reset is issued, and thereafter a sequence of code particular to the keyboard type in use is executed. Reset must therefore always be issued after changing the keyboard type.
When using an ASCII encoded alphanumeric keyboard monitor commands are typed in as shown in this chapter. There is however, no reset key on an ASCII keyboard, one must be fitted as shown in the chapter describing assembly of the microtan kit. TANBUG drives this type of keyboard in the interrupt mode.
The keypad is used somewhat differently, its layout being shown below.
TANBUG interrogates the keypad for a depressed key, then translates the matrix encoded signal into an ASCII character which it puts up on the visual display just as if the equivalent key were depressed on an ASCII encoded keyboard. Because of the limited number of keys it has been necessary to incorporate a shift function on the keypad. So, to obtain the character P for example, the user presses and releases SHIFT, then depresses and releases P. The SHIFT key contains a self cancelling facility - if the user presses SHIFT twice in succession the pending shift operation is cancelled. So as an example, using the two keys SHIFT and 8 the operations SHIFT P yields P on the display. SHIFT SHIFT P yields 8 on the display. Other special purpose keys on the keypad are RST, which issues a reset to the microtan, and DEL which deletes the last character typed. Repeated deletes erase characters back to the beginning of the line.
SHIFT DEL LF SPCR RST M
0 1 2 ,
From now on in this chapter the microtan will be treated as having one type of keyboard only, since all functions required can be derived by depressing the appropriate key or keys on whatever is used - keyboard or keypad.
Having described some of the background to TANBUG it is now possible to describe the commands and syntax of TANBUG i.e. how to use it. An example is shown later on. All numerical values of address, data and monitor command arguments are in hexadecimal. The symbol <CR> means on depression of the carriage return key, <SP> the space key or bar, <ESC> the escape key (ALT on some keyboards) and <LF> line feed. In all examples, text to be typed by the user will be underlined, while TANBUG responses will not. indicates the cursor. <ADDR> means a hexadecimal address, <ARG> means hexadecimal data and <TERM> means one of terminators <CR>, <SP>, <ESC> or <LF>.
All commands are of the form
<COMMAND><TERM>where <COMMAND> is one of the mnemonic commands and <ARG> is a hexadecimal argument applicable to the command being used. The required argument is defined for each command. It should be noted at an early stage that the longest argument will contain 4 hexadecimal characters. If more are typed all but the last 4 are ignored. As an example consider the memory modify command M12340078 <CR>. In this case location 0078 will be modified or examined as all but the last 4 characters are ignored.
or <COMMAND><ARG>, <ARG><TERM>
or <COMMAND><ARG>, <ARG>, <ARG><TERM>
<TERM> is one of the terminating characters <CR>, <SP>, <LF> or <ESC>. In fact TANBUG accepts any of the "control" characters (HEX code 0-20) as terminator. TANBUG will reply with a ? if an illegal command is encountered.
Starting the monitor TANBUG:
Press the RST key on the keypad or the reset key or button connected
to the microtan. TANBUG will scroll the display and respond with
Note that on initial power up the top part of the display will be filled with spurious characters. These will disappear as new commands are entered and the display scrolls up. On subsequent resets the previous operations remain displayed to facilitate debugging.
Memory modify/examine command M:
The M command allows the user to enter and modify programs by changing the RAM locations to the desired values. The command also allows the user to inspect ROM locations, modify registers etc. To open a location type the following
M <ADDR><TERM>TANBUG then replies with the current contents of that location. For example to examine the contents of RAM location 100 type M100<CR>
M100,0E,assuming the current contents of the location were 0E.
There are now several options open to the user. If any terminator is typed the location is closed and not altered and the cursor moves to the next line scrolling up the display by one row. If however, a value is typed followed by one of the terminators <CR>, <LF> or <ESC> the location is modified and then closed. For example using <CR>
M100,0E,FFlocation 100 will now contain FF. If however <SP> is typed, the location is re-opened and unmodified.
M100,0E,FFThis facility is useful if an erroneous value has been typed. The terminators <LF> and <ESC> modify the current location being examined, then opens the next and previous locations respectively
M100,0E,FFand using <ESC>
M100,0E,FFUsing <LF> makes for very easy program entry, it only being necessary to type the initial address of the program followed by its data and <LF>, the responding to the cursor prompt for subsequent data words.
NOTE that locations 1FE and 1FF should not be modified. These are the stack locations which contain the monitor return addresses. If they are corrupted TANBUG will almost certainly "crash" and it will be necessary to issue a reset in order to recover.
List command L:
The list command allows the user to list out sections of memory onto the display. It is possible to display the contents of a maximum of one hundred and twenty consecutive memory locations simultaneously. To list a series of location type
L <ADDR>, <NUMBER><TERM>where <ADDR> is the address of the first location to be printed and <NUMBER> is the number of lines of eight consecutive locations to be printed. TANBUG pauses briefly between each line to allow the user to scan them. For example, to list the first 16 locations of TANBUG (which resides at FC00-FFFF) type LFC00,2<CR>.
LFC00,2If zero line are requested (i.e. <NUMBER> = 0) then 256 lines will be given.
FC00 A2 FF 9A E8 86 17 20 B7
FC08 FF 8D F3 BF A2 0E BD DF
Go command G:
Having entered a program using the M command and verified it using the L command the user can use the G command to start running his own program. The command is of the format G <ADDR><TERM>. For example, to start a program whose first instruction is at location 100 type G100<CR>. When the user program is started the cursor disappears. On a return to the monitor it re-appears.
The G command automatically sets up two of the microprocessors internal registers
a) The program counter (PC) is set to the start address given in the G commandThe contents of the other four internal registers, namely the status word (PSW), index X (IX), index Y (IY) and accumulator (A), are taken from the monitor pseudo registers (described next). Thus the user can either set up the pseudo registers before typing the G command, or use instructions within his/her program to manipulate them directly.
b) The stack pointer (SP) is set to location 1FF.
Register modify/examine command R:
Locations 15 to 1B within the RAM reserved for TANBUG are the user pseudo registers. The user can set these locations prior to issuing a G command. The values are then transferred to the micro-processors internal registers immediately before the user program is started. The pseudo register locations are also used by the monitor to save the user internal register values when a breakpoint is encountered. These values are then transferred back into the microprocessor when a P command is issued, so that to all intents and purposes the user program appears to be uninterrupted.
The R command allows the user to modify these registers in conjunction with the M command. To modify/examine registers type R<CR> and the following display will appear (location 15 containing 00 say)
RNow proceed as for the M command.
Naturally the M command could be used to modify/examine location 15
without using the R command - the R command merely saving the user the
need to remember and type in the start location of the pseudo registers.
Pseudo registers locations are as follows.
|15||Low order byte of program counter (PCL)|
|16||High order byte of program counter (PCH)|
|17||Processor status word (PSW)|
|18||Stack pointer (SP)|
|19||Index X (IX)|
|1A||Index Y (IY)|
Two typical instances of the use of the R command are:-
a) Setting up PSW, IX, IY and A before starting a user program.Note that when modifying registers in case (b) care must be taken if PCL, PCH or SP are modified, since the proceed command P uses these to determine the address of the next instructions to be executed (PCL, PCH) and the user stack pointer (SP).
b) Modifying registers after a breakpoint but before proceeding with program execution (executing the P command) for debugging purposes.
Single instruction mode S:
Single instruction mode is a very powerful debugging aid. When set TANBUG executes the user program one instruction at a time, re-entering the monitor between each instruction and printing out the status of all of the microprocessor's internal registers as they were after the last instruction executed in the user program. The S command is used in conjunction with the proceed command P and the normal mode command N. Examples are given in the description of the P command.
Normal mode command N:
The N command is the complement of the S command and is used to cancel the S command so that the microprocessor executes the user program in the normal manner without returning to the monitor between each instruction. Reset automatically sets the normal mode of operation.
Proceed command P:
The P command is used to instruct TANBUG to execute the next instruction in the user program when in single instruction mode. Pseudo register contents are transferred into the microprocessors internal registers and the next instruction in the users program is executed. The monitor is then re-entered. P may also be used with an argument thus P <NUMBER><CR> where NUMBER is less than or equal to FF. In this case the program executes the specified number of instructions before returning to the monitor.
Each time the monitor is re-entered after execution of an instruction or instructions, the status of the microprocessor internal registers as they were in the user program are printed across the screen in the following order:
Address of next instruction to be executed.Note that these are in the same order as the pseudo registers described earlier.
Processor status word.
Index register X.
Index register Y.
Whenever the user program is entered, the cursor is removed from the display. Whenever the monitor is entered, the cursor returns to the display as a user prompt. While in the monitor between user instructions, any monitor command can be typed. A program must always be started by the G command, then P used if in single instruction mode. A P command used before a G command is issued is likely to cause a program "crash" and should not be attempted.
As an example consider the simple program which repeatedly adds 1 to
|100||69||ADC #1||add 1 to acc|
Set the single instruction mode and start the program. The user may wish to initially set the accumulator to 00 by using the M command.
STANBUG then responds with the characters shown above.
0102 20 FF 00 00 01
0102 is the address of the next instruction to be executed.Since the cursor has re-appeared, TANBUG is ready for any monitor command. For example, registers or memory locations can be modified, or the program may be re-started from scratch by typing G100<CR> again. If the user wishes to continue then type P<CR>. The resulting display is
20 is the processor status word value.
FF is the low byt value of the stack pointer. The high byte is always set to 1, the stack is therefore pointing at location 1FF.
00 is the value of the index X register.
00 is the value of the index Y register.
01 is the value of the accumulator. It is a 1 as 1 has been added to the accumulator and it is assumed that the user cleared the accumulator before starting the program.
SSince the instruction at location 102 was "Jump to 100", the status print out shows that this has indeed occurred. Registers, since they were not modified by any program instruction, remain unchanged. To proceed further type P<CR> again.
0102 20 FF 00 00 01
0100 20 FF 00 00 01
SThe add instruction has been executed again, so the accumulator has incremented by 1 to become 2. Now typing P4 <CR> gives a display.
0102 20 FF 00 00 01
0100 20 FF 00 00 01
0102 20 FF 00 00 02
STANBUG allowed execution of 4 instructions before again returning to the monitor. The 4 instructions were 2 add instructions and 2 jump instructions thus giving the accumulator the value 4.
0102 20 FF 00 00 01
0100 20 FF 00 00 01
0102 20 FF 00 00 02
0102 20 FF 00 00 04
By typing N<CR> then P<CR> removes the single instruction mode and causes the program to proceed. It now does not return to the monitor but continues to race around this small program loop continually adding and jumping back. There is no way to exit from this trivial program except by a microprocessor reset or, if using an alphanumeric keyboard, by typing ESC.
It can be seen that the S and P commands are particularly useful when tracing a program which contains instructions that transfer program control e.g. jumps, branches and subroutines, since these commands allow the user to interrogate the order of execution of his/her program.
Breakpoint command B:
A breakpoint is a complementary debugging aid to single instruction mode. Instead of stepping singly through all instructions in a program, the breakpoint facility allows the user to specify the address at which he requires the monitor to be re-entered from his/her program. As an example, consider a long program in which a fault is suspected to exist near the end. It would be very tedious and time consuming to single step through the program to the problem area. A breakpoint can be set just previous to where the fault is suspected to exist and the program started with the G command. Normal execution occurs until the breakpoint is reached, then the monitor is re-entered with the same status print-out as for single instruction mode. Any monitor commands can then be used and the program continued.
The format of the breakpoint command is
B <ADDR>, <NUMBER> <CR>where <ADDR> is the address of any instruction OPCODE (but not argument), <NUMBER> is any number from 0-7 defining one of 8 breakpoints. B <CR> removes all breakpoints. As an example consider the following program
Firstly set index X, index Y and the accumulator to 00 using the R command. To set breakpoint 0 at the jump instruction and start the program type B104,0<CR>. The display will then be
100 E8 LOOP: INX 101 C8 INY 102 C9 01 ADC #1 104 4C 00 01 JMP LOOP
B104,0The jump instruction was reached and the breakpoint re-directed control back to TANBUG. If it were required, single instruction mode could be set for further debugging. However, assume that we wish to execute the loop again by typing P<CR>.
0104 20 FF 01 01 01
B104,0The proceed command P has gone once through the breakpoint and then re-entered the monitor. If P<NUMBER><CR> was typed it would have proceeded through the breakpoint <NUMBER> times.
0104 20 FF 01 01 01
0104 20 FF 02 02 02
Up to 8 breakpoints can be set at 8 different locations. The B <CR> command removes all breakpoints. A single breakpoint can be removed by setting its address to 0. For example, imagine a breakpoint is set as follows; B102,2, and it is subsequently wished to remove it but leave any others unaltered; type B0,2<CR> to remove it.
Caution. The breakpoint system works by replacing the users instruction with a special instruction (BRK) whose opcode is 00. Replacement is carried out when G or P is typed. On return to the monitor the original opcode is replaced. It is therefore possible to corrupt the user program under some circumstances. The following points should therefore be observed:
a) Breakpoints must only be set at the opcode part of a user instruction and nowhere else.The status of breakpoints may be inspected by using the M command to examine the breakpoint status table. This is located in RAM locations 20-2F and are as follows:
b) If the user program utilises the BRK instruction as part of the user code, then the user must have his own special interrupt routine and cannot use breakpoints.
c) If breakpoints are set in the user program and a reset is issued while the microprocessor is executing the user program rather than the monitor, the breakpoints are lost and those locations at which breakpoints were set in the user program will be corrupted. These locations must be re-entered using the M command before restarting the user program.
d) Setting more than one breakpoint at the same address causes the user program to be corrupted.
e) To use breakpoints, the user must not have modified the interrupt link, i.e. the interrupt code within TANBUG must be executed.
For example, typing M20<CR> followed by <LF> gives
Address Contents 20 PCL B0 21 PCH B0 22 PCL B1 23 PCH B1 24 PCL B2 25 PCH B2 26 PCL B3 27 PCH B3 28 PCL B4 29 PCH B4 2A PCL B5 2B PCH B5 2C PCL B6 2D PCH B6 2E PCL B7 2F PCH B7
M20,00,This indicates that breakpoint 0 is set to location 100 by taking the contents of location 20 as PCL and of location 21 as PCH. If the breakpoint is set at location 0 then this particular breakpoint is disabled.
Offset command O:
The offset command O is a program writing aid. It calculates branch offsets for the user for incorporation as arguments in branch instructions. Consider the example:-
To calculate the number to enter into location 121 is quite tedious without a facility such as the O command. It is used with the following format.
100 E8 LOOP: INX 101 C8 INY 102 69 ADC #1 103 01 . . . 120 D0 BNE LOOP 121 (branch argument)
O <ADDR. OF BRANCH OPCODE><ADDR. OF DEST.><CR>and in this case it would be necessary to type O120,100<CR>. The display would be
O120,100 = DEDE is the number that should be entered into location 121 such that if the BNE instruction is true the program counter will jump to the label LOOP.
Note that the maximum branch range is 7F forwards and backwards. If the range is exceeded a ? is displayed.
Copy command C:
The copy command allows copying of the contents of one block of memory to another. Its format is
C <START ADDR. SOURCE><END ADDR. SOURCE><START ADDR. DEST>Suppose it is required to copy the block of data in locations FC00-FD00 into a block starting at location 200. This may be achieved by typing CFC00,FD00,200<CR>. The display will be
CFC00,FD00,200As 200 is the starting address of the display memory the user will notice that the top half of the screen has been over written with all sorts of weird and wonderful characters. What this example has done is to take the first 256 bytes of TANBUG and copy them into the top half of the display. The display then scrolled having the top 7 rows filled with these characters.
Breakpoints and the ESC key
If an alphanumeric keyboard is being used, depression of the ESC key (ALT on some keyboards) will cause a re-entry into the monitor from the user program. This is possible because the alphanumeric keyboard is interrupt driven. For example, if the trivial program
has been started by typing the G command the program continues to loop around continuously with no exit path to the monitor, except by issuing a reset. Instead of a reset the user can press the ESC key, TANBUG responding thus
100 69 LOOP: ADC #1 101 01 102 4C JMP LOOP 103 00 104 01
0100 20 FF 01 01 01Using the ESC key has caused a breakpoint to be executed and the monitor invoked. The register print-out above is only typical, the value of each beaing that when the ESC was depressed. Any monitor command may now be typed, for example P causes the user program to proceed once again.
The ESC facility is most useful in debugging where the user program
gets into an unforseen loop where breakpoints have not been set. It enables
the user to rejoin the monitor withour using reset and losing the breakpoints
that have been set.
a) The ESC facility is only implemented on interrupt driven keyboard i.e. alphanumeric ASCII keyboards, and is not implemented on the keypad.USER SUBROUTINES
b) Interrupts must be enabled for the ESC facility to operate. TANBUG enables interrupts when entering a user program, therefore do not disable interrupts if the ESC facility is required.
c) The user must not have modified the interrupt jump link. TANBUG's interrupt code must be executed.
Certain input/output subroutines are available to the user.
these rely on a standard display format, this will be described
first, followed by the user subroutine descriptions.
TANBUG uses the bottom line of the display for all text operations.
Initially the cursor is at the left hand edge of the screen, and
moves gradually to the right as a line is filled. When either a
carriage return is output, or the bottom line overflows, the display
is scrolled (all lines shift up one row) and the bottom line becomes
available for more output. Therefore the cursor always remains on
the bottom line. However, there is no reason why users should
restrict themselves to this mode of operation unless they intend to
use TANBUG's subroutines to control the display in their own
programs. It should be noted that the display memory is read/
write memory and may be used as a character buffer prior to
processing thus saving RAM locations for a user program.
Subroutine POLLKB is used to interrogate the keyboard for a
key. (Appropriate software for the type of keyboard in use is
automatically set-up by TANBUG when a reset is issued). On exit
from the subroutine the RAM location labelled ICHAR (address W01)
contains the ASCII code of the character typed, whether it is typed
on the keypad or on an alphanumeric keyboard. When using the
alphanumeric keyboard, interrupts must be in the enabled state.
As an example consider the user code
1) C LI
2) JSR POLLKB poll the keyboard
3) LDA ICHAR load acc. with character
The sequence of operations here are
1) Enable interrupts so that alphanumeric keyboard may
2) The program loops around within the POLLKB sub-
routine until a key is pressed.
3) The program exits from POLLKB with the -ASCII code
for the key pressed in the location label-led ICHAR.
The accumulator is loaded with this value.
Notes: Address of subroutine POLLKB is FDFA. Address of ICHAR is
W01. The registers IX, IY and A are corrupted, therefore the user
must save and restore their values if necessary.
subroutine causes the display to scroll up one line by out-
putting a carriage return to it. It also reinstates the cursor,
which is switched off when a user program is started. This sub-
routine should be called in a user program prior to any display
input or output to clear the bottom line.
Notes: Address of subroutine OUTPCR is FE73. Registers IX and IY
are unaffected. Register A is corrupted and must be saved if
re quire d.
subroutine is called to output a character held in the
accumulator, to the display. The cursor, obliterated on a user
program start, is re-instated. As an example, consider the code
Since 30 is the ASCII code for the character "Oll and 31 is the
ASCII code for the character 11111, the result (assuming this is the
first call to this subroutine) on the botbom line of the display is
Repetitive calls of OPCHR will fill the bottom line of the display
with the appropriate characters. When the end of the line is
reached, OPCHR scrous the display up one line and then writes
characters in the newly vacatbd bottom line and so on.
Notes: Address of subroutine OPCHR is FE75. Registers IX and IY
are unaltered. Register A is corrupted and must be saved if
re quire d.
Subroutine HEXPNT takes a binary value from the accumulator and
outputs it as two hexadecimal characters on the display. Consider
save A on stack
JSR OUTPCR scroll display
PLA recover A
JSR HEXPNT output A in hex
JSR OUTPCR scrol 1 display
This code will display the contents of the accumulator as two hex
characters. For example if the accumulator contained the value 2C
the resulting display would be
Notes: Address of subroutine HEXPNT is FFOB. Register IY is
unaltered. Registers IX and A are corrupted and must be saved if
re quire d.
This subroutine reads hex characters from the bottom line of the
display and packs them up into two eight bit binary values,
enabling a sixteen bit word to be assembled. It is useful for
incorporation into programs which require numerical keyboard input.
Usually POLLKB is used in conjunction with OPCHR to enter data to
the display, then HEXPCK called when a carriage return is
encountered. The following user code could be used to do this
scrol 1 display
NXTCHR: JSR POLLKB wait for chwacte r
LDA ICHAR put it in A
CMP# $0D carriage return ?
EE Q GOPACK yes, p ack it
JSR OPCHR else store in display
JM P NXTCHR get next character
1) GOPACK: LDY# 00 set IY to first char.
2) JSR HEXPCK pack it
In this example the subroutine is used in the following way:
1) Set IY with the character position at which
packing is to start. The left most location of the
bottom line corresponds to setting IY tc) 0. The
next location corresponds to IY equal to 1 etc.
2) Call HEXPCK. Characters are packed until a
character other that 0-9 or A-F is encountered; an
exit then occurs.
3) Continue into the user code where the values of
HXPKL and HXPKH will be read.
For example, packing 1 CR gives HXPKL = 1 and HXPKH = 0.
Packing FEDC CR gives HXPKL = DC and HXPKH = FE. Packing
FEDCBA CR gives HXPKL = BA and HXPKH = DC, i.e. if more than
four hexadecimal characters in succession are encountered then the
last four are packed. Additionally, two flags in the processor
status word (PSW) are used to indicate exit conditions. The zero
flag Z is clear if the terminating character is the cursor (ASCII
code FF), set otherwise. The overflow flag V is set if there w as
one or more hex characters, clear if the first character encountered
by the subroutine was not a hexadecimal character.
Notes: Address of subroutine HEXPCK is FF28. Address of HXPKL is
is 0013 and HXPKH is 0014. Registers IX, IY and A are all
corrupted and must be saved if necessary.
TANBUG uses both the maskable and non-maskable interrupts.
ever, means have been provided tc) access the interrupts via both
hardware and software. Of necessity user interrupts may, in some
cases, place restrictions on certain monitor commands.
The maskable interrupt
When TANBUG is initialised by a reset, certain RAM locations are
set up to link through the interrupts for monitor use. These
locations are labelled INTFS1, INTFS2, INTFS3 and INTSL1. When a
maskable interrupt occurs, the following sequence of events is
obeyed (assuming the RAM locations mentioned above have not been
a) The program jumps to INTFS1 in RAM.
b) The locations INTFS1, INTFS2 and INTFS3 contain
the instruction JMP KBINT. The program therefore
jumps to KBINT which resides in the monitor ROM.
c The monitor software looks to see what caused the
interrupt. If a BRK instruction, then the break-
point code is executed. If a keyboard interrupt,
location ICHAR is updated with the new ASCII
character which is read from the keyboard I/O
d) If the interrupt is caused by anything other than
a BRK instruction then the monitor jumps to
e) Normally INTSLL contains an RTI instruction - the
program would then return to where it was
It can therefore be seen that the user can implement his/her own
interrupt service routines in two ways.
1) A fast interrupt response by modifying the
locations INTFS1, INTFS2 and- INTFS3 to jump to the
user interrupt service code. In this case bre ak-
points and the ESC command cannot be used unless
the u--er program jumps back to the monitor service
routine after executing its own code.
2) A slower interrupt response by modifying INTSL1,
INTSL2 and INTSL3 to jump to user service routine,
after executing the monitor service routine. The
RAM locations INTSL1, INTSL2 and INTSL3 would be
modified to contain the instruction JMP USER. This
method places no restrictions on monitor commands.
of things should be noted when using interrupts:
a) An RTI instruction must always occur at the end of
user code to return the program to the point at
which it was interrupted, unless the user code
jumps back to the monitor service routine.
b) If a reset it issued, the INTFS and INTSL locations
are set back to their monitor values by TANBUG,
and the user has to reset them.
c) If any microprocessor internal registers are used
in the user interrupt service routine, they must be
saved before modification and restored before the
RTI instruction, i.e. on return to the monitor the
registers IX, IY and A must contain the same
values as they had on entry to the user routines.
d) The interrupt jump locations should be modified by
instructions in the user program at run time and
not by the use of the M command. This is because
TANBUG softwar\-- uses keyboard interrupts. If
using an alternative link at INTFS1, no break-
points c an be set.
e Addresses of RAM locations are; INTFS1 = OW4,
INTFS2 = OW5, INTFS3 = ON6, INTSLI 0010,
INTSL2 = 0011, INTSL3 = 0012.
The non-maskable interrupt
interrupt vector is accessed in the same way as
explained for the maskable interrupt. The user can obtain access
by modifying locations NMIJP, NMIJPL and NMIJP2. Note that single
instruction mode will be inoperative and that breakpoints will be
destructive, i.e. they are destroyed when they have been executed
once and replaced with the original code. Addresses of RAM
locations are; NMIJP = OW7, NMIJPL and NMIJP2 = W09.
It will be noted that TANBUG displays a question mark whenever an
illegal command is typed. In order to allow future expansion of
the monitor, an error link to memory external to the monitor ROM's
When an error occurs the following sequence of events is initiated:
a) The program jumps to F7F7.
b) With no expansion board (TANEX) present the
address F7F7 (outside TANBUG space) is decoded as
address FFF7 (inside TANBUG space).
c) A question mark is printed.
With TANEX present, a special link is incorporated to return the
program to the monitor. The user may remove this link and insert
an EPROM in the position which includes the address F7F7
containing the code JMP USERCODE at address F7F7, where USERCODE
may contain software to deal with any extra commands the user
wishes to add to the monitor. Note that this facility will be used
by future TANGERINE software.
There are two methods of returning to the monitor from external
1) The instruction RTS at the end of the user code
returns to the monitor, gives a carriage return
then continues looking for commands.
2) The instruction JMP FFF7 returns tc) the monitor,
giving a question mark on the display.
EXAMPLE OF TANBUG's USE
The following, simple example program clears the screen by calling
OUTPCR F times, then slowly fill the screen with asterisks. It is
used as an example to demonstrate the use of some of TANBUG's
commands. Deliberate errors are later writben into the program to
demonstrate TANBUG's fault finding capabilities.
The first step in writing a program is to produce a flowchart of
program execution. The second step is to write the program in
assembly language code using the instruction mnemonics. The third
to look up and write the op-codes and arguments for each
instruction. At this stage the branch code arguments will be left
blank and TANBUG's 0 command used.
and program listing now follows.
Example program listing
0050 00 00
; display index
0052 AO OF START: LDY# F ;set Y index
0054 20 73 FE SCRAG: JSR OUTPCR ;carriage return
0057 88 DEY ;do E times
0058 10 (arg 1) BPL SCRAG
005A A9 20 LDA# 20 ;load A ascii space
005C 8D EO 03 STA 3EO ;obliterate cursor
005F , A9 00 LDA# 0 ;set display index
0061 85 50 STA VDUIND
0063 A9 02 LDA# 2
0065 85 51 STA VDUIND+L
0067 AO 00 CONT: LDY# 0 ;clear Y index
0069 A9 2A LDA# 2A ;set ascii
006B 91 50 STA (VDUIND),y
006D A2 OF LDX# F ; delay loop
006F AO FF LDY# FF
0071 88 DECIT: DEY
0072 DO (arg 2) BNE DECIT
0074 CA DEX
0075 DO (arg 3) BNE DECIT
0077 18 CLC ;inc display index
0078 E6 50 INC VDUIND
007A Do (arg 4) BNE NOMSB
007C E6 51 INC VDUIND+L
007E A5 51 NOMSB: LDA VDUIND+L ;top of display?
0080 C9 03 CMP# 3
0082 Do (arg 5) BNE CONT ; no - continue
0084 A5 50 LDA VDUIND
0086 C9 FF CMP# FF
0088 DO (arg 6) BNE CONT ; double prec. cmp.
008A 00 BRK ;return to monitor
Program entry is performed using the M command.
For the time
being set the branch arguments (arg I - arg 6) to 00, these c an be
altered when calculated, using the 0 command.
Once the program is entered the branch offsets are calculated.
first is arg 1 which has an opcode address of 0058 and branches to
the label SCRAG at location 0054. By typing 058,54<CR> TANBUG
print3 out the value of arg 1 as FA. This may now be placed in
location 0059 using the M command. By repeating the exercise for
the other five arguments it will be found that location 0073 should
contain FD, 0076 should contain FA, 007B should contain 02, 0083
should contain E3 and 0089 should contain DD.
The program will now run if it has been entered correctly.
start the program type G52<CR> since the first instruction of the
program is at location 0052. When the screen is full of asterisks
the program exits to the monitor. Alternatively, if an alphanumeric
keyboard is being used, depression of the ESC key causes an exit
to the monitor. If the program does not run correctly then it may
be necessary to issue a reset in order to regain control. The
program can be listed by typing L50,8<CR> yielding a display of
0050 00 00 AO OF 20 73 FE 88
0058 10 FA A9 20 8D EO 03 A9
0060 00 85 50 A9 02 85 51 AO
0068 00 A9 2A 91 50 A2 OF AO
0070 FF 88 DO FD CA DO FA 18
0078 E6 50 DO 02 E6 51 A5 51
0080 C9 03 DO E3 A5 50 C9 FF
0088 DO DD 00 XX XX XX XX XX
providing the program has been correctly entered (XX indicates any
value as these locations are not part of the program). If the
program failed to run carefully check the listing from the L
command with the program listing and correct any errors with the M
Having got the program working it is now possible to introduce a
deliberate error to demonstrate the use of breakpoints and the
single instruction mode. The error to be introduced is to put the
wron value for the branch argument on the first occurrence of the
instruction BNE DECIT; instead of location 73 containing FD change
it to F B. Now the register IY will never be zero and the program
will loop here. If the program is started now only one asterisk
will be printed and then nothing else will happen. Debugging
steps are as follows:
a) Regain control to the monitor by issuing a reset.
b) The first part of the program is being executed
correctly as the display scrolls. Furthermore, it
is at least getting to location 6B because an
asterisk is printed. It would be very tedious to
single instruction this far from the beginning
because the OUTPCR routine is called sixteen times.
Therefore set a breakpoint at location 6D by typing
c) Start the program again by typing G52<CR>. The
display scrolls and the status message
006f 31 F F OF 00 2 A
is displayed. Control is now back in the monitor.
d) Set single instruction mode by typing S<CR>.
e) Repeatedly typing P<CR> causes single instructions
to be executed followed by a status print-out. The
following sequence of instructions will be, observed.
006F 21 FF OF 00 2A
0071 Al FF OF FF 2A
0072 Al FF OF FE 2A
006F Al FF OF FE 2A
Now if the code were correct the program could not
go back to location 6F. In fact, since IY is
shown to be FE, the program should have jumped
back to location 71. The branch instruction is
probably at fault, therefore examine it and its
argument using the M command.
The value in location 73 should be FD, therefore
change it by typing FD<CR>.
f) Remove single instruction mode and breakpoints by
typing N<CR> then B<CR>.
g) Restart the program by typing G52<CR>. The
program should now run correctly.
that when using an alphanumeric keyboard, debugging is
slightly easier. When the program stlcks in a loop ESC can be
used to return to the monitor (provided interrupts have not been
disabled). Single instruction mode can then be set to determine
the loop in which the program was running.
TABLE OF HEX ASCII CODES
01 Control A Home
02 Control B
03 Control C
04 Control D
05 Control E
06 Control F
07 Control G Bel 1
08 Control H Backspace
09 Control I Horizontal Tab - Cursor Right
OA Control J Line Fee d
OB Control K
oc Control L P age Cle ar - Form Fee d
OD Control M Carriage Return
OE Control N
OF Control 0
10 Control P
11 Control Q
12 Control R
13 Control S
14 Control T
15 Control U
16 Control V
17 Control W
18 Control X
19 Control Y
1A Control Z Vertic al Tab Cursor Up
Note that the codes 00 - 1F produce special symbols when used
in display memory.
TABLE OF HEX ASCII CODES (CONTINUED)
21 41 A 61 a
22 42 B 62 b
23 f- or 43 c 63 c
24 $ 44 D 64 d
25 % 45 E 65 e
26 & 46 F 66 f
27 47 G 67 9
28 48 H 68 h
29 49 I 69 i
2A 4A i 6A
2B 4B K 6B k
2C 4C L 6C 1
2D 4D m 6D m
2E 4E N 6E n
2F 4F 0 6F 0
30 0 50 p 70 p
31 1 51 Q 71 q
32 2 52 R 72 r
33 3 53 s 73 s
34 4 54 T 74 t
35 5 55 u 75 u
36 6 56 v 76 v
37 7 57 w 77 w
38 8 58 x 78 x
39 9 59 y 79 y
3A 5A z 7A z
3B 5B 7B
3C < 5C 7C
3D 5D 7D
3E > 5E A 7E
3F ? 5F 7F or Rubout
;reserved for bpt use
Owl ICHAR: 00 ; asci-i character
ON2 OCHAR: 00 ;temp char store
W03 VDUIND: 00 ; display index
OW4 INTFS1: 00 ;fast int link
OW5 INTFS2: 00
OW7 NMIJP: 00 ;nmi link
OW8 NMIJP1: 00
W09 NMIJP2: 00
OMA ICURS: 00 ;cursor index
OMB ICURSH: 00 ;cursor index high
moc RUNIND: 00 ; zero if in user
OND SINGLE: 00 ; nonzero if sing int3
OOOE PROCED: 00 ; proceed count
OMF SIMCOM: 00 ;simple/complex kb
0010 INTSL1: 00 ; slow int i nk
0011 INTSL2: 00
0012 INTSL3: 00
0013 HXPKL: 00 ;hexpack low byte
0014 HXPKH: 00
0015 PCLBCK: 00 ;pseudo reg PCL
0016 PCHBCK: 00 PCH
0017 PSWBCK: 00 ; PSW
0018 SPBCK: 00 ;SP
0019 XBCK: 00 ;IX
001A YBCK: 00 ;IY
001B ABCK: 00 ; A
ooic MODADL: 00 ;temp store
001D MODADH: 00
001E COPL: 00 ; copy store
001F COPH: 00
0020 BPTLO: 00 ; bpt status table
0023 BPTHL: 00
002 C 00
002 F 00
0030 BPTCOD: 00 bpt code store
0100 STKBSE: 00 ;stack base address
0200 VDUSTT: 00 ;display scroll labels
0220 VDUFST: 00
0300 VDUMID: 00
0320 VDUTOP: 00
03EO LINBOT: 00
BFFO SGRAPH: 00 ;I/O ports
KBINCL: 00 ;alt. tc) SGRAPH
BFF1 SNMI: 00
BFF2 KBWRIT: 00
BFF3 KBREAD: 00
STEXT: 00 ;alt. to KBREAD
F7 lF7 INPERR: 00 ;error exit link
;start of main program init. sequence
;program starts here on a reset
START: LDX #FF
;set stack pointer
FC02 9A TXS ;to top of the stack
F C03 EN, INX ;enable interrupts in
FC04 8617 STX PSWBCK user prog on a go
;clear breakpoint store as their values will be
;indeterminate on power up.
FC09 8DF3BF STA STEXT ;set text mode.
now use table to initiate parameters
;note order of table must correspond with the
;order of INTFS1 to ICURSH in ram definitions.
FCOE BDDFFF SETUPL: LDA SETUPX ; get value.
FC11 9504 STA INTFS1, X ; store in ram.
FC13 CA DEX
FC14 10FO BPL SETUP1 ; do till all done
; determine keyboard type and set flag
; note IX=FF.
FC16 EO INX
FC17 8E90FO TSFIV: STX KBWRIT ;clear kb write latch.
FCLA 8DFOBF STA KBINCL ;clear kbint. flag.
FCLD CA DEX
FCLE 8EF2BF STX KBWRIT ; write to kb lines.
FC21 EO INX ;reset IX.
FC22 ADF3BF LDA KBREAD ;read it back.
FC25 1002 BPL KPCPLX ;if plus not set-alpha.
FC27 E60F INC SIMCOM ;if set then keypad.
FC29 8DFOBF KPCPLX: STA KBINCL ;clear kbint.
FC2C BDECFF TBMS: LDA HDR, X ; print TANBUG.
FC2F F006 BEQ MONTOR
FC31 2075FE JSR OPCHR ;o/p chars until a 0.
FC34 E8 INX
; monitor at present part of main program.
FC37 D8 MONTOR: CLD ;set binary mode.
FC38 58 CLI
FC39 20FAEO JS R POLLKB ; look at kb.
FC3C A501 LDA ICHAR ;get char.
FC3E C921 CMP #21 ;LT or EQ space-term.
FC40 3006 BMI MONCH1 ;else o/p char.
FC42 2075FE ISTERM: JSR OPCHR
FC45 4C37FC JM P MONTOR
FC48 204FFC M ONCHL: JSR M ONEN2 ;call string process.
FC4B A90D RCl: LDA #D ;set up CR.
FC4D DOF3 BNE ISTERM ;uncond. branch loop.
FC4F Aooo M ONEN2: LDY #0 ; set IY to zero.
FC51 B10A LDA (ICURS), Y ;pick up command.
FC53 AA TAX ; store in X.
FC54 Co INY ; pee k at ne xt c h ar.
FC55 B10A LDA (ICURS), Y ;get it in A.
FC57 1036 BPL MULTI ;if -ve was curs or.
FC59 A900 LDA #0 ;else set A to zero.
FC5B E053 TRYS: CPX #53 ; was it S?
FC5D D003 BNE TRYM ; yes-set GT 0 else skip.
FC5F 860D STX SINGLE
FC61 60 RTS
FC62 E04E TRYN: CPX #4E ; was it N?
FC64 D003 BNE TRYP ; no-try P.
FC66 850D STA SINGLE ;else clr single mode.
FC68 60 RTS
FC69 E050 TRYP: CPX #50 ; P with no ar g?
FC6B D004 BNE TRYR ; no-try for R.
FC6D 850E STA PROCED ;else clr P count.
FC6F F056 BEQ PROC1 ;uncond. branch proc.
FC71 E052 TRYR: CPX #52 ;command R?
FC73 D009 BNE TRYB ;no-try for no bpts.
FC75 851D STA MODADH
FC77 A915 LDA #15 ;else set pseudo reg.
FC79 851C STA MODADL
FC7B 4CE5FD JMP REOPEN ;jmp mod memory.
TRYB: CPX #42
FC80 D004 BNE ERRQ ;no-error.
FC82 2OB7FF JSR BPTCLR ;else clear.
FC85 60 RTS
; with no TANEX FFF7 will respond to F7F7.
;with TANEX monitor can be expanded.
;FFF7 jumps back to here.
FC86 4CF7F7 ERRQ: JMP !NPERR
FC89 A93F RETERR: LDA #3F ;load question mark.
FC8B 2075FE JSR OPCHR ;print it.
FC8E 60 PRERC: RTS
;if we get here command expects data too.
FC90 8A TXA ;save cmd on stack.
FC91 48 PHA
FC92 202OFF JSR HEXPCK ; pack its arg.
FC95 D054 BNE MOREY ; more data?
FC97 68 PLA ;else is cmd G.
FC98 50EC BVC ERRQ ;error if no arg.
FC9A C947 CMP #47 ;is it a G?
FC9C D021 BNE TRYPL ; no-s kip.
FC9E A200 LDX #0
FCAO 860E STX PROCED ;clr proceed count.
FCA2 CA DEX ;set IX to FF.
;if G stack pointer initialised
;and pseudo registers loaded.
FCA4 A514 LDA HXPKH push PC high.
FCA6 48 PHA
FCA7 LDA HXPKL push PC low.
FCA9 48 PHA
FCAA A517 LDA PSWBCK
FCAC 48 PHA
FCAD C60C DEC RUNIND ;cl-r run flag.
FCAF A920 LDA #20 ;obliterate cursor.
FCB3 910A STA (ICURS), Y
FCB5 A619 LDX XBCK
FCB7 A41A LDY YBCK
FCB9 A51B SRET: LDA ABCK ; set users A.
FCBB 8DFlBF STA SNMI ;set NMI for next.
FCBE 40 RTI ; get to user prog.
FCBF C950 TRYPL: CMP #50 ;is cmd P with arg?
FCC1 DOll BNE TRYM ; no-try M.
FCC3 A513 LDA HXPKL ; else set P count.
FCC5 850E STA PROCED
FCC7 A516 PROCL: LDA PCHBCK ;restore users PC.
FCC9 8514 STA HXPKH
FCCB A515 LDA PCLBCK
FCCD 8513 STA HXPKL
FCCF A618 LDX SPBCK ;set IX tc) users SP.
FCD1 4CA3FC JMP GOEND ;then back ti) user.
FCD4 C94D TRYM: CMP #4D ; is it M address?
FCD6 DOAE BNE ERRQ ; no-error popping S.
FCD8 A92C EQPT: LDA #2C
FCDA 2075FE JSR OPCHR
FCDD AWO LDY #0 ; pick up value
FCDF B113 LDA (HXPKL), Y
FCE1 20OBFF JSR HEXPNT ;and print it.
FCE4 68 PLA ; pop stack return.
FCE5 68 PLA
FCE6 A92C LDA #2C ;load comma.
FCE8 4C42FC JMP ISTERM ;back to monitor.
FCEB E02C MOREY: CPX #2C ;was term a comma?
FCED F004 BEQ GETPT2 ;yes-continue.
FCEF 68 LINKPH: PLA ;else pull command
FCFO 4C86FC LINKR: JMP ERRQ ;and give error.
FCF3 A513 GETPT2: LDA HXPKL ; no-stc)re previous
FCF5 851C STA MODADL ;in MODADL&MODADH.
FCF7 A514 LDA HXPKH
FCF9 851D STA MODADH
FCFB 2028FF JSR HEXPCK ; p ac k ne xt v alue.
FCFE D07C BNE MOREY1 ; not curs-more yet.
FDOO 68 PLA ;else pull command.
FDO1 50ED BVC LINKR ; no arg? - error.
;is it L?
FDO5 F042 BEQ LISTIT ; yes-list it.
FDO7 C94F CMP #4F ; is it offset O?
FDO9 D027 BNE TRYBPT ; no-skip.
FDOB A513 LDA HXPKL ;else get branch dest.
FDOD 38 SEC
FDOE E902 SBC #2 ;adj for branch code.
FDlo B002 BCS NOTOPO
FD12 3OA0 DEC HXPKH
FD14 38 NOTOPO: SEC
FD15 E51 C SBC MODADL ; subtract source.
FD17 AA TAX ; hold result in IX.
FD18 A514 LDA HXPKH ; subtract high byte.
FDLA E51D SBC MODADH
FDLC A8 TAY ; store in I Y.
FDLD 8A TXA ; get low byte.
FDLE 3005 BMI RNGNG ; if -ve branch.
FD20 98 TYA ; if +ve look at high.
FD21 DOCD BNE LINKR ;not O-error.
FD23 F003 BEQ PNTITO if ok continue.
FD25 C8 RNGNG: INY if -ve high is FF.
FD26 DOC8 BNE LINKR
FD28 A93D PNTITO: LDA #3D ;ok-print equals
FD2A 2075FE JSR OPCHR
FD2D 8A TXA
FD2E 20OBFF JSR HEXPNT ;and the value.
FD31 60 RTS
FD32 C942 TRYBPT: CMP #42 ;is it B?
FD34 DOBA LINK1: BNE LINKR ;no-error.
FD36 2898 LDA HXPKL ;max bpt code is 7.
FD38 3OB6 BMI LINKR
FD3A C908 CMP #8 ; if greater-error.
FD3C 1OB2 BPL LINKR
FD3E OA ASL A ; double A.
FD3F AA TAX ;set X for mode X.
FD40 A51C LDA MODADL ;store bpt address.
FD42 9520 STA BPTLO, X
FD44 A51D LDA MODADH
FD46 9521 STA BPTH, X
FD48 60 JPRTRN: RTS
FD49 2073FE LISTIT: JSR OUTPCR ;o/p carriage return.
FD4C AOM LDY #0 ;set IY to zero.
FD4E A51D LDA MODADH ; print address.
FD50 2009FF JSR HEXPNT
FD53 A51C LDA MODADL
FD55 2009 F F NXLIST: JSR HEXPNT ;o/p low byte.
FD58 A920 LDA #20 -load a space.
FD5A 2075FO JSR (PDCHR ;o/p 8 mem locations.
FD5D B11C LDA (MODADL), Y ;get character.
FD5F C8 INY
FD60 C009 CPY #9 ; is IY GT 7?
FD62 3OF1 BMI NXLIST ; no-more yet.
FD64 C613 DEC HXPKL ;dec line count.
;note that requesting 0 lines gives 256!
FD66 FOEO BEQ JPRTRN ;O? RTS via CR.
FD68 88 DELX1: DEY
FD69 DOFD BNE DELXL
FD6B CA DEX
FD6C DOFA BNE DELXL
;now adjust the address.
FD6E A51C LDA MODADL ;get low bybe.
FD70 18 CLC
FD71 6908 ADC #8 ;add 8.
FD73 851C STA MODADL store it.
FD75 9OD2 BCC NXLI more if C set.
FD77 E61D INC MODADH inc high byte.
FD79 4C49FD JMP NXLI
; if we get here there is a third parameter.'
FD7C E02C M OREYL: CPX #2C ;term a comma?
FD7E F018 BEQ TERMOK ;no-error..
FD80 4CEFFC ERJUM2: JMP LINKPH
FD83 A513 TERMOK: LDA HXPKL ;else store parameter.
FD85 851E STA COPL
FD87 A514 LDA HXPKH
FD89 851F STA COPH ;then pack new para.
FD8E DOFO BNE ERJUM2 ; error not term I d.
FD90 68 PLA ;is command M?
FD91 C94D CMP #4D
FD93 F027 BEQ MEM100 ; yes-mod memory.
FD95 C943 CMP #43 ; is it C?
FD97 D09B BNE LINK1 ;no-error.
; if copy command, start address is held in MODADL.
;end address in COPL.
;destination address in HXPKL.
FD99 5099 BVC LINK1 ;arg? error if not.
FD9B AOM LDY #0
FD9D B11C NXCOP: LDA (MODADL), Y ;get instruction.
FD9F 9113 STA (HXPKL), Y ; store it.
FDAL A51F LDA COPH ;is it done?
FDA3 28E8 CMP MODADH
FDA5 D006 BNE ICMCOP
FDA7 A51E LDA COPL
FDA9 C51C CMP MODADL
FDAB F05B BEQ ENDLS
FDAD E61C ICMCOP: INC MODADL increment source.
FDAF D002 BNE NOHIH1
FDBL E61D INC MODADH
FDB3 E613 NOHIH1: INC HXPKL ;increment dest.
FDB5 DOE6 BNE NXCOP
FDB7 E614 INC HXPKH
FDB9 DOE2 BNE HXCOP
;destination can not roll over top of memory.
;return if end.
FDBC A601 MEM100: LDX ICHAR ; get term char in IX.
FDBE E020 CPX #20 ;was it a space?
FDCO F023 BEQ REOPEN ; yes-reopen.
FDC2 5006 BVC NOENT ; branch if nothing.
FDC4 A513 LDA HXPKL ;else enter data.
FDC6 PM LDY #0
FDC8 911C STA (MODADL), Y
FDCA EOOA NOENT: CPX #A ;was LF typed?
; yes-process it.
FDCE E018 CPX #lB, ; was it ES C?
FDDO D036 ENDLS ;no-return.
FDD2 C61C ESCIT: DEC MODADL ; dec mem mod address
FDD4 A51C LDA MODADL
FDD6 C9FF CMP #FF
FDD8 D009 BNE REOPEN
FDDA C61D DEC MODADH
FDDC 4CE5FD JMP REOPEN
FDDF E61C WASLF: INC MODADL ; inc mem address.
FDE1 D002 BNE REOPEN ;also high byte.
FDE3 E61D INC MODADH
FDE5 2073FE REOPEN: JSR OUTPQR ;o/p carriage return.
FDE8 A94D LDA #4D
FDEA 2075FE JSR OPCHR ;print M.
FDED A51D LDA MODADH ; print address.
FDEF 20OBFF JSR HEXPNT
FDF2 A51C, LDA MODADL
FDF4 20OBFF JSR HEXPNT
FDF7 4C4FFC JMP MONEN2 go to cm d bit.
; note all addresses are page zero.
FDFA A900 POLLKB: LDA #0
FDFC 48 PHA ; push 0-shift ind.
FDFD 8501 PLKB1: STA ICHAR ;set ICHAR to zero.
FDFF C50F CMP simcom ;is it,keypad?
FE01 D006 BNE SIMPLE
FE03 C501 WAIT1: CMP ICHAR ;else wait for int.
FE05 FOFC BEQ WAIT1
FE07 68 PLKEND: PLA pop in dic atc)r.
FE08 60 ENDLS: RTS
;simple keypad routine.
FE09 A90F SIMPLE:
;enable all kb lines.
FEOB 8DF2BF STA KBWRIT
FEOE ADF3BF LDA KBREAD look at kb nes.
FEll DOF6 BNE SIMPLE ;key down?-wait ti-li up.
FE13 A240 LDX #40 ; debounce it.
FE16 DOE8 BNE DEBOUN
FE18 CA DEX
FE19 DOFA BNE DEBOUN
;now poll the keypad properly.
;note IY is zero.
PLK1: LDY #FF
;set up Y index.
FELD 68 PLA ; peep at shift ind.
FELE 48 PHA
FELF F002 BEQ NOSHIF ;if shift set mod IY.
FE21 A013 LDY #13
FE23 A208 NOSHIF: LDX #8 ;set IX-kb drive.
FE25 8EF2BF PLK2: STX KBWRIT ;drive kb lines.
FE28 ADF3BF LDA KBREAD ;get result in A.
FE2B DOOC BNE ACHAR ;not 0-a char-skip.
FE2D C8 INY ;else adjust IY.
FE2E C8 INY
FE2F C8 INY
FE30 C8 INY
FE31 C8 INY
FE32 8A TXA ;shift IX right.
FE33 4A LSR A
FE34 AA TAX
FE35 FOE4 BEQ PLK1 ;if zero repeat.
FE37 DOEC BNE PLK2 ;else next line.
if we get here a key has been pressed.
FE3A 4A LSR A ;which key of 5?
FE3B 90FC BCC ACHAR ; C set'? thats key.
FE3D B94BFE LDA CHRTBL, Y ; get asc ii e quiv.
FE40 8501 STA ICHAR put it in IACHR.
FE42 DOC3 BNE PLKEND ; if zero-shift.
FE44 68 PLA ; pull shift.
FE45 49FF EOR #FF ;change shift state.
FE47 48 PHA ; push shift.
FE48 4CO9FE JMP SIMPLE ; continue.
;character look up table for ascii equivalent.
FE4B 333742 CHRTBL:
FE58 44 OA
;output character routine.
;on entry character is stor\--d in A.
I X an d I Y are s ave d.
FE73 A90D OUTPCR:
; load CR.
FE75 8502 OPCHR: STA OCHAR ;save the character.
FE77 8A TXA ;save IX and IY.
FE78 48 PHA
FE79 98 TYA
FE7A 48 PHA
FE7B A403 LDY VDUIND ;get curs position.
FE7D A920 LDA #20 ;obliterate cursor.
FE7F 910A STA (ICURS), Y
FE81 A602 LDX OCHAR ;get char in IX.
FE83 E07F CPX #7F ; is it delete?
FE85 D010 BNE TRYCR ;no-skip.
FE87 88 DEY ;else dec vdu index.
FE88 1002 BPL DODEL ;if neg set zero.
FE8A AOM ZERCUR: LDY #0
FE8C A9FF DODEL: LDA #FF ; print cursor.
FE8E 910A STA (ICURS), Y
FE90 8403 STY VDUIND ;save index.
FE92 68 PLA ;restore regs and rtn.
FE94 68 PLA
FE95 AA TAX
FE96 60 RTS
FE97 EOOD TRYCR: CPX #D ; is it a C R?
FE99 F008 BEQ DOCR ;yes-process it.
FE9B 8A TXA ;else o/p character.
FE9C 910A STA (ICURS), Y
FEGE C8 INY ;inc vdu index.
FE9F C020 CPY #20 ; end of line?
FEAL 3OE9 BMI DODEL ; no-tidy up-exit.
FEA3 A200 DOCR: LDX #0 ;else scroll.
FEA5 BD2002 LOWBLK: LDA VDUFST, X ; do in two blocks.
FEA8 9@2 STA VDUSTT, X
FEAB E8 INX
FEAC DOF7 BNE LOWBLK
FEAE BD2003 HIBLK: LDA VDUTOP, X
FEB1 9WW3 STA VDUMID, X
FEB4 E8 INX
FEB5 EOEO CPX #Eo ; see if done.
FEB7 DOF5 BNE HIBLK
FEB9 A920 LDA #20 ;fi.-ll line spaces.
FEBB A8 TAY
FEBC 88 M ORSP: DEY ; set IX as count.
FEBD 910A STA (ICURS), Y
FEBF DOF'B BNE MORSP ;do for whole line
FEC1 FOC7 BEQ ZERCUR ;when done tidy up.
;keyboard interrupt subroutine.
;note this is entered via jump instruction
;stored in RAM location labelled INTF'SL
;so that user can access interrupts quickly.
;a reset will always initiahse INTFS1.
FEC4 D8 CLD ;set binary mode.
FEC5 8A TXA ;save IX.
FEC6 48 PHA
FEC7 BA TSX ; get SP in IX.
FECB E8 INX ; IX tc) add old PSW.
FEC9 E8 INX
FECB BDO001 LDA STKBSE, X ;get the PSW.
FECE 2910 AND #10 w as it a bre ak?
FEDO DOLE BNE BRKP yes-process it.
FED2 68 PLA ;else pull IX.
FED3 AA TAX ;restz)re and continue.
FED4 ADF3BF LDA KBREAD ;read keyboard.
FED7 3004 BMI WASKB if -ve w as kb.
FED9 68 USER: PLA else restore A.
FEDA 4ClWo JM P INTSLL
;note that INTSLL normally holds an RTI
;unless the user has modified it.
FEDD 297F WASKB:
; mask top bit.
FEDF 8501 STA ICHAR ; put it in ICHAR.
FEE1 8DFOBF STA KBINCL ;clr kb int flip-flop.
FEE4 C91B CMP #lB ; w as it ES C?
FEE6 DOF1 BNE USER ; no-norm al return.
FEE8 A50C LDA RUNIND ;user prog running?
FEEA DOED BNE USER ; no-norm a-1.
FEEC 850E STA PROCED ;else clr pr-oc count.
FEEE F012 BEQ ACTBP ;uncond br to break.
;break processing code-break was encountered.
; note the user should not set a break at own break
;or in this interrupt routine else crashes.
;now adjust PC to return to instr must subtract 3.
; address PC L.
FEF1 38 SEC ;set C.
FEF2 BDOW1 LDA STKBSE, X ; get PCL.
FEF5 E902 SBC #2 ; subtract 3.
FEF7 9DOW1 STA STKBSE, X ;put it back.
FEFA B004 BCS NOROLL ; C set? NOHI byte.
FEFC E8 INX ;else address PCH.
FEFD DEN08 DEC STKBSE, X ; dec PCH.
FFOO 68 NOROLL: PLA ;pull IX.
FF01 AA TAX ; restore it.
FF02 68 ACTBP: PLA ;pull accumulator.
FF03 851B STA ABCK ;back it up.
;restore user code.
FF08 4C75FF NOROL: JMP NMNT1 service break.
;HEXPNT takes a hex value stored in accumulator
;ie a two character number and displays it.
;registers are not saved. IX is corrupted.
;save value of char.
FFOC A201 LDX #1 ;load IX with 1.
FFOE 4A LSR A ; get top part
FFOF 4A LSR A ;by multiple shifts.
FF10 4A I-SR A
FF11 4A LSR A
FF12 18 PNT2: CLC
FF13 6930 ADC #30 ;add hex 30.
FF15 C93A CMP #3A more than 9?
FF17 3003 BMI PNT1 no- print it.
FF19 18 CLC
FFLA 6907 ADC #7
FFLC 2075FE PNT1: JSR OPCHR ;print it.
FFLF CA DEX
FF20 lool BPL MOR1 ;-ve?-end else low bit.
FF22 60 RTS
FF23 68 MORL: PLA ;recover low bits.
FF24 29OF AND #F ;clr unwanted bits.
FF26 10EA BPL PNT2 ;uncond branch.
;HEXPCK uses values in TXTP to store hex
;of characters indexed by IY from display RAM.
;on exit, caused by any non-hex character,these
;contain a two byte number. HEXENT contains
;the number of characters entered.
;registers are not saved.
;on exit IY points tc) the last character.
;the zero flag is clear if the terminating
;character was the cursor, else set.
;the overflow flag is set if this subroutine
;encountered some hex data.
FE28 A900 HEXPCK:
FF2A 48 PHA ;push as PSW.
FF2D 8514 STA HXPKH
FF2F CB NXHX: INY
FF30 B10A LDA (ICURS), Y ;get character.
FF32 AA TAX ; store in I X
FF33 38 SEC ;subtract hex 30.
FF34 E930 SBC #30 ; tc) give 0 to 9.
FF36 3010 BMI ENDTS
FF38 C90A HX1: CMP #A ; is it 0 tc) 9?
FF3A 3010 BMI HX2 ;yes-pack it.
FF3C 38 SEC ;else sub hex 11.
FF3D E911 SBC #11
FF3F 3007 BMI ENDTS ;goto carry setup.
FF41 18 HX3: CLC ;else add 9.
FF42 690A ADC #A
FF44 C910 CMP #10 ;more than 15? exit.
FF46 3004 BMI HX2
FF48 28 ENDTS: PLP ;deal with V flag.
FF49 EOFF CPX #FF ; c ursor.
FF4B 60 RTS
note character is in IX on exit
;return does not affect zero flag.
HX2: LDX #4
; its he x s ave it.
FF4E 0614 HX5: ASL HXPKH ; shift left 4 times.
FF50 0613 ASL HXPKL ;add new one.
FF52 9002 BCC HX4
FF54 E614 INC HXPKH ; replicate.
FF56 CA HX4: DEX ; dec IX until zero.
FF57 DOF5 BNE HXS
FF59 18 CLC ; add in char.
FF5A 6513 ADC HXPKL
FF5C 8513 STA HXPKL ; store it.
FF5E 68 PLA ; get pseudo PSW.
FF5F A940 LDA #40 ; set V bit.
FF61 48 PHA ;and push it.
FF62 DOCB BNE NXHX ; do next.
;non-maskable interrupt routine for single instr.
FF64 851 B
NMNT: STA ABCK
FF66 D8 CLD ;set binary mode.
FF67 A50D LDA SINGLE ;test single inst.
FF69 DOOA BNE NMNT1
FF6B 8A TXA ; if not save I X.
FF6C 48 PHA
FF6D 20DOFF JSR BPSET ;set breakpoints.
FF70 68 PLA ;restore IX.
FF71 AA TAX
FF72 A51B LDA ABCK ;restore accumulator.
FF74 40 RTI
FF75 A50E NMNT1: LDA PROCED ;get proc count.
FF77 F005 BEQ ZERBCK ;if zero break.
FF79 C60E DEC PROCED ;else dec count.
FF7B 4CB9FC JMP SRET ;rts via single test.
FF7E E60C ZERBCK: INC RUNIND ;set not running.
FF80 68 PLA ; pop bpt PSW to acc.
FF81 8517 STA PSWBCK ;back it up.
FF83 68 PLA
FF84 8515 STA PCLBCK ; ditto PC L.
FF86 68 PLA
FF87 8516 STA PCHBCK ; ditto PC H.
FF89 8619 STX XBCK
FF8B 841A STY YBCK
FF8D BA TSX ;operators SP.
FF8E 8618 STX SPBCK
FF90 2073FE PSEUD: JSR OUTPCR
FF93 A516 LDA PCHBCK
FF95 20OBFF JSR HEXPNT
FF98 A515 LDA PCLBCK
FF9A 20OBFF JSR HEXPNT
FF9D AWO LDY #0 ;clear IY.
FF9F A920 PSNX: LDA #20 ;print two spaces.
FFAL 48 PHA
FFA2 2075FE JSR OPCHR
FFA5 68 PLA
FFA6 2075FE JSR OPCHR
FFA9 B91700 LDA PSWBCK, Y
FFAC 20OBFF JSR HEXPNT
FFAF C8 INY ;do all registers.
FFBO C005 CPY #5
FFB4 4C4BFC JMP RC1
;breakpoint clearing routine uses IX and A.
FFB7 A21F BPTCLR:
; set count for 8 bpt3.
FFB9 A900 LDA #0
FFBB 9520 BPTCL1: STA BPTLO, X ; c le ar a loc atio n.
FFBD CA DEX ; dec count.
FFBE 10FB BPL BPTCL1 ; do for all loc atio ns.
FFCO 60 RTS
;this subroutine removes breakpoints by
;writing back the users original code.
;IX and IY are used.
FFC2 48 PHA
FFC3 A20E LDX #E ; set for 8 bpts.
FFC5 B530 BPTRML: LDA BPTCOD, X ;load old instruction.
FFC7 8120 STA (BPTLO, X) ;write tc) prog mem.
FFC9 CA DEX
FFCA CA DEX ;decrement it.
FFCB 10 BPL BPTRM1 ;do for all bpts.
FFCD 68 PLA
FFCE AA TAX
FFCF 60 RTS
;subroutine BPSET looks at the entered breakpoint
;addresses, stores the present instruction
;and writes brk to program memory.
BPSET: LDX #E
; set for 8 bpts.
FFD2 A120 BPS1: LDA (BPTLO, X) ;get users instr.
FFD4 9530 STA BPTCOD, X ; store it.
FFD6 A900 LDA #0 ;set brk..
FFD8 8120 STA (BPTLO, X)
FFDA CA DEX
FFDB CA DEX
FFDC 1OF4 BPL BPS1 ;do tlll done.
FFDE 60 RTS
;setup table for initial values.
;order is same as RAM locations.
FFDF 4CC3FE SETUP:
;header message "TANBUG"
FFF7 4C89FC JMP RETERR
Start Address: B0
No options required.
Life is a program which simulates a colony of living organisms
which can grow, move and die out. "Life" is run in two stages.
1) Seeding the cells. On starting the program, the display is
cleared and the cursor is placed in the middle of the
screen. Four single letber commands are avail-able to move
the cursor about the lower half of the display.
L moves it to the left.
R moves it to the right.
D moves it down.
M moves it up.
A fifth command, A, whenever typed replaces the cursor with
an asterisk, which then remains on the display when the
cursor is moved again. By using these five commands any
patbern of asterisks can be built up on the lower half of
2) Evolution. Typing "GI' causes the program to jump from the
seeding mode and into the evolution mode. Every two seconds
the display is scanned and a new "generation" of cells
produced from the old according to the following rules.
a) If a cell space is surrounded by exactly three other
asterisks, this cell will contain an asterisk in the next
b) If an asterisk is surrounded by two or three others, it
will remain as an asterisk in the next generation.
c) All- other arterisks will become spaces.
Eventually a stable patbern will occur which will either be an
immobile patbern, a blinking pattern or a blank screen. At this
point the monitor can be entered by issuing a reset or, if using an
alphanumeric keyboard, by depressing ESC and a new game started.
Note that asterisks placed on the bottom line of the display do not
change; they act as a permanent seeding set.
life pro gr am
OOAO VDULO: ; vdu position.
0OA2 YIND: ; y i-idex.
OOBO Aolo LDY #10 ;clear screen.
0OB2 2073FE NXSR: JSR OUTPCR
0OB5 88 DEY
0OB6 DOFA BNE NXSR
0OB8 A920 LDA #20 ;obliterate cursor.
OOBA 8@E003 STA CUR
OOBD AOW LDY #0 ; put curs in mid vdu.
OOBF 84AO STY VDULO
00cl LDY #3
0OC3 84Al STY VDUHI
0OC5 AOOF LDY #F
0OC7 84A2 NXC: STY YIND
0OC9 A9FF L-DA #FF
OOCB 91 AO P LKI T: STA (VDULO), Y
OOCD 20FAFD JSR POLLKB
OODO A4A2 LDY YIND ;char--cursor?
OOD2 BlAo LDA (VDULO), Y
OOD4 C9FF CMP #FF
OOD6 D008 BNE NODL ; no-skip.
OOD8 A920 LDA #20 ;else delete.
OODA 91 AO STA (VDULO), Y
OODC 4CEOW JMP NODL ;skip for expansion.
OOEO A601 NODL: LDX ICHAR ;pick up input char.
OOE2 E04C CPX #4C ; L for left?
OOE4 D006 BNE NOL ;no-skip.
OOE6 88 DEY
OOE7 DODE BNE NXC ;look for 'next command.
OOE9 C8 INGO: INY ; else inc it.
OOEA DODB BNE NXC ; unconditional branch.
OOEC E052 NOL: CPX #52 ; R for right?
OOEE D006 BNE NOLL ; no-skip.
OOFO COLE CPY #lE ;else shift right.
; next char.
0OF4 DOF3 BNE INGO
0OF6 E041 NOLL: CPX #41 ; A for asterisk?
0OF8 D004 BNE NOL2 ; no-skip.
OOFA A92A LDA #2A ; e lse o utp ut a
OOFC DOCD BNE PLKIT ; unconditional branch.
OOFE E@ NOL2: CPX #44 ; D for down?
0100 DOOA BNE NOL3 ; no-skip.
0102 18 CLC ;else inc line pointer.
0103 A5AO LDA VDULO
0105 6920 ADC #20
0107 85AO STA VDULO
0109 4CC700 JMP NXC
010C E04D NOL3: CPX #4D ; M for up?
010E DOOA BNE NOL4 ; no-s kip.
0110 38 SEC ;else sub a line.
0111 A5AO LDA VDULO
0113 E920 SBC #20
0115 85AO STA VDULO
0117 4CC700 LKAG: JMP NXC
01 1 A @Z047 NOLA: CPX #47 ; G for go?
011C DOF9 BNE LKAG ; no-skip.
011E AOW GO: LDY #0
0120 84AO STY VDULO
0122 A002 LDY #2
0124 84Al STY VDUHI
0126 A900 GOTW 0: LDA #0 determine number
0128 85A2 STA YIND ;of cell neighbours.
012A A920 LDA #20
012C A207 LDX #7
012E BC3COl NXX: LDY INDEX, X
0131 DlAo CMP (VDULO), Y
0133 F002 BEQ DCT
0135 E6A2 INC YIND
0137 CA DCT: DEX
0138 1OF4 BPL NXX ;YIND holds number.
013A 3008 BMI CNT
013C 000102 INDEX:
0144 18 CNT: CLC ;clear carry.
0147 C903 CMP #3 ; if 3 go set carry.
0149 FOOC BEQ CST
014B C902 CMP #2 ;if not 2 clear carry.
014D D058 BNE CNS1
014F A021 LDY #21 if 2 look at this.
0151 BLAO LDA (VDULO), Y
0153 C920 CMP #20
0155 F050 BEQ CNS1
0157 38 CST: SEC ; c arry set if in ne xt.
0158 A250 CNS: LDX #50 ; store it shift prev.
015A 3640 NXPL: ROL LIN1, X
015C CA DEX
015D 10FB BPL NXPL
015F E6AO INC VDULO do for whole page.
0161 D002 BNE NHI
0163 E6Al INC VDUHI
0165 A5Al NHI: LDA VDUHI
0167 C903 CMP #3
0169 D006 BNE TPJP
016B A5AO LDA VDULO
016D C9BE CMP #BE
016F F03A BEQ PATCH1
0171 4C2601 TPJP: JMP GOTWO
0174 38 DNUPD: SEC ;empty store tD vdu.
0175 E901 SBC #1
0177 85AO STA VDULO
0179 A5Al LDA VDUHI
017B E900 SBC #0
017D 85Al STA VDUHI
017F 4CB001 JMP PATCH2
0182 EA NOP
0183 A220 DLYIT: LDX #20 ;delay.
0185 88 DLDY: DEY
0186 DOFD BNE DLDY
0188 CA DEX
0189 DOFA BNE DLDY
018B 4ClEol JMP GO
018E A200 MOROP: LDX #0
0190 A050 LDY #50
0192 7640 NXROR: ROR LIN1, X
0195 88 DEY
0196 10FA BPL NXROR
0198 A920 LDA #20
019A 9002 BCC CHROP
019C A92A LDA #2A
019E ANO CHROP: LDY #0
OLAO 91AO STA (VDULO), Y
OlA2 A5AO LDA VDULO
OlA4 4C7401 JMP DNUPD
OlA7 18 CNS1: CLC
OlA8 4C5801 JMP CNS
01AB A9DF PATCHL: LDA #DF
01AD 4C7401 JMP DNUPD
01 BO C902 PATCH2: CMP #2
OIB2 DODA BNE MOROP
01 B4 A5AO LDA VDULO
01 B6 C920 CMP #20
01 B8 DOD4 BNE M OROP
01BA FOC7 BEQ DLYIT
Start Address: 0045
No options required.
A row of "aircraft" fly across the screen fiom left to right. A
"gun" is positioned at the bottom of the display. Typing any key
causes the gun to shoot at the aircraft. Number of shots and
number of hits are recorded. The object of the game is tc) shoot
all the aircraft down with the minimum number of shots.
When all aircraft are shot down, the game is automatically re-
started after a delay.
;aircraft line delay.
0041 GUNDL: ; gun delay.
0042 SHOOT: ; shoot flag.
0043 GNPOSL: ; gun position.
0045 AOOF START: LDY #F ;clear screen.
0047 2073FE INITCR: JSR OUTCR
004A 88 DEY
004B IOFA BPL INITCR
004D A920 LDA #20
004F 8DE003 STA SCRTP
0052 A01A LDA #lA ;write aircraft to line 2.
0054 A9FF LDA #FF
0056 994002 NXAC: STA AC, Y
0059 88 DEY
005A 88 DEY
005B 88 DEY
005C 1OF8 BPL NXAC ; set up delay.
005E 8540 STA LINDL
0060 A930 LDA #30 ; zero the scale.
0062 8D2002 STA VDUT
0065 8D2102 STA VDUT1
0068 Aool RESGUN: LDY #1 ;reset gun delay.
006A 8441 STY GUNDL
006C 88 DEY ;clear ICHAR.
006D 8401 STY ICHAR
006 F A50F LDA SIMCOM ; if full kb skip.
0071 FOOA BEQ FULLK
0073 A90F LDA #F ;if keypad wait no key.
0075 8DF2BF STA KBWRIT
0078 ADF3BF W T: LDA KBREAD
007B DOFB BNE W T
007D 8442 FULLK: STY SHOOT ;clear shoot flag.
007F AOEF LDY #EF ;set gun position.
0081 8443 STY GNPOSL
0083 A003 LDY #3
0085 8444 STY GNPOSH
0087 ANO ACDLY: LDY #0 ;actually put it out.
0089 A95E LDA #5E
STA (GNPOSL), Y
008D AOFF MSDLY: LDY #FF ; master delay.
008F 88 GMDL: DEY
0090 DOFD BNE GMDL
0092 C640 DEC LINDL ; dec aircraft delay.
0094 D015 BNE ROTEND ; not O go test shoot.
0096 A960 LDA #60 ;else reset delay.
0098 4C3101 JM P PATCH1 ; rotate ne.
009B 48 BACK: PHA
009C A01 E LDY #lE
009E B94002 ROTRT: LDA SRTLIN, Y
0OAl 994102 STA SRPLUS, Y
0OA4 88 DEY
0OA5 1OF7 BPL ROTRT
0OA7 68 PLA
0OA8 8D4002 STA LINBT
OOAB A542@ ROTEND: LDA SHOOT ; shoot in progress?
OOAD D023 BNE GOSHOT ;yes-deal with it.
OOAF A50F LDA SIMCOM ;else keypad?
0OB1 D006 BNE SIMKBL ; yes-branch.
0OB3 A501 LDA ICHAR ;else full kb hit?
0OB5 FOD8 BEQ GMDL ; no-w ait.
0OB7 D005 BNE INSHT ; else go and shoot.
0OB9 ADF3BF SIMKB1: LDA KBREAD ; look at kb.
OOBC FOD1 BEQ GMDL
OOBE E642 INSHT: INC SHOOT ; hit-inc in dic atc)r.
OOCO EE2102 INC VDUT1 ; adjust shots @d.
0OC3 AD2102 LDA VDUT1
0OC6 C93A CMP #3A
0OC8 3008 BMI GOSHOT
OOCA A930 LDA #30
OOCC 8D2102 STA VDUT1
OOCF EE2002 INC VDUT
OOD2 C641 GOSHOT: DEC GUNDL ; dec gun delay.
OOD4 DOB7 BNE MSDLY ; not O then more delay.
OOD6 A91 F LDA #lF ;else reset gun delay.
OOD8 8541 STA GUNDL
OODA PM LDY #0 ;obliterate gun.
OODC JMP NXLL ;skip for expansion.
OOEO A920 NXLL: LDA #20
STA (GNPOSL), Y
OOE4 38 SEC
OOE5 A543 LDA GNPOSL ;adjust gun position.
OOE7 E920 SBC #20
OOE9 8543 STA GNPOSL
OOEB B002 BCS NOHIH
OOED C644 DEC GNPOSH
OOEF A902 NOHIH: LDA #2 ;gun in aircraft rank?
0OF1 C544 CMP GNPOSH
0OF3 D092 BNE ACDLY no-continue.
0OF5 A94F LDA #4F
0OF7 C543 CMP GNPOSL
0OF9 D08C BNE ACDLY else we are.
OOFB AD4FO2 LDA GNLN ;have we scored?
OOFE C9FF CMP #FF
0100 F003 BEQ AHIT ;a hit-deal with it.
0102 4C6800 JMP RESGUN ;else reset gun.
0105 A920 AHIT: LDA #20 ;obliterate aircraft.
0107 8D4FO2 STA GNLN
010A AD2502 LDA ACSCO ;setup the score.
Olot D C920 CMP #20
01OF D008 BNE INCSC
0111 A931 LDA #31
0113 8D2502 STA ACSCO
0116 4C6800 RSJP: JMP RESGUN
0119 EE2502 INCSC: INC ACSCO
011C C938 CMP #38 ; game over test.
011E DOF6 BNE RSJP
0120 A909 LDA #9 ; delay, then restart.
0122 8543 STA GNPOSL
0124 CA DLY: DEX
0125 DOFD BNE DLY
0127 88 DEY
0128 DOFA BNE DLY
012A C643 DEC GNPOSL
012C DOF6 BNE DLY
0131 8540 PATCHL: STA T.TNDL
0133 AD5FO2 LDA ENDLN
0136 4C9BOO JMP BACK
Calling Address: OW (not relocatable)
Variables: XCOORD O"
Requirements: Graphics option.
subroutine uses the VDU as a 64 x 64 pixel graphics
display. When called it picks up the values of X and Y co-
ordinates (set up by the calling program) and turns the relevant
pixel on. The bottom left hand side of the screen is point (0,O).
Note that this
subroutine does not turn any pixel off - it is
therefore necessary to zero the screen before using this subroutine
to output a graph.
Notes on use of graphics subroutine.
1) Initially with the monitor in "TANBUG", all unused areas of
the screen are filled with spaces (HEX 20). Before attempting
to draw a graph using the subroutine shown, the screen must
be filled with hex O's with graphics mode set.
2) If using TANBUG and graphics mode, test mode is not reset
on entering TANBUG. Care must therefore be taken that the
program resets text mode before exit.
3) The OPCHR subroutine should not be used if graphics mode is
in use anywhere on the screen.
4) It is possible to display both alphanumerics and graphics
characters simultaneously, e.g. an annotated graph. The
procedure is as follows:- a) set graphics mode, b) fill
screen with hexadecimal O's, c) draw axes and graph,
d) set text mode, e) write text.
Note that any use of the OPCHR subroutine, e.g. by the monitor,
corrupts the graphics display.
this subroutine this example program also contains a
main program which utllises it. The program repeatedly draws X
and Y axes and the function y = Y2x.
Start address: FD
0041 00 YCOORD:
0042 00 VDULO:
OW ADFOBF GRAPH: LDA GON ;set graphics mode.
0047 A93 F LDA #3F ;check coord size.
0049 C540 CMP XCOORD
004B 302E BMI EXIT
004D EA NOP
004E 38 SEC
004F E541 SBC YCOORD
0051 EA NOP
0052 48 PHA
0053 2903 AND #3 ; m ask tc) 2 lsbs.
0055 AA TAX ; store in I X.
0056 68 PLA
0057 EA NOP
0058 293C AND #3C ; mask two lsbs.
005A OA ASL A ; shift 1 3 times.
005B OA ASL A
005C OA ASL A
005D 8542 STA VDULO
005F A902 LDA 92 ; set up VDULO and
0061 8543 STA VDUHI ; VDUHI with y axis
0063 9002 BCC NOINC ; address.
0065 E643 INC VDUHI
0067 A54 0 NOINC: LDA XCOORD ; get xcoordinate.
0069 4A LSR A
006A A8 TAY ; adjust, store in I Y
006B A901 LDA #1 ; determine which
006D 9001 BCC NOSF2 ;bit to set in the
006F OA ASL A ; graphics'word
0070 'CA NOSF2: DEX ; held in acc.
0071 3004 BMI ENDOP
0073 OA ASL A
0074 OA ASL A
0075 DOF9 BNE NOSF2 jm p to re pe at.
0077 1142 ENDOP:
ORA (VDULO) Y
;or with present.
0079 9142 STA (VDULO), Y ;write it back out.
007B 60 ;EXIT: RTS fig
;this program repeatedly draws X and Y axes
;and the function y=?/2x to demonstrate the
;operation of the 'graphics subroutine and the
; graphics hardware.
;first save regs, o/p graph subroutine and delay.
0084 48 SAVOP: PHA
0085 98 TYA
0086 48 PHA
0087 8A TXA
0088 48 PHA ;save registers.
0089 A220 LDX #20 ;set delays.
008B AOW LDY #0
008D 88 DECM: DEY
008E DOFD BNE DECM
0090 CA DEX
0091 DOFA BNE DECM
0093 2@ JSR GRAPIA ;output char.
0096 68 PLA restor-e.
0097 AA TAX
0098 68 PLA
0099 A8 TAY
009A 68 PLA
009B 60 RTS
OOFD ADFOBF LDA GON ;set graphics mode.
0100 A900 GTEST: LDA #0 ;clear display.
0102 AA TAX
0103 9DWO2 NXSTO: STA VDUL, X
0106 9DWO3 STA VDUM, X
0109 CA DEX
010A DOF7 BNE NXSTO
010C EA NOP
010D A03F LDY #3F ;set IY decimal 63.
01OF A900 LDA #0 ;clear x co-ord.
0113 8441 NEX: STY YCOORD ;load IY to y co-ord.
0115 208400 JSR SAVOP ;o/p char with delay.
0118 88 DEY do for y axis ne.
0119 1OF8 BPL NEX
011B A03F LDY #3F now do for x axis.
011D 8541 STA YCOORD
011F 8440 NEX1: STY XCOORD
0121 208400 JSR SAVOP
0124 88 DEY
0125 1OF8 BPL NEX1
0127 A200 LDX #0 now draw graph.
0129 8640 NXT: STX XCOORD
012B 8A TXA
012C 4A LSR A
012D 8541 STA YCOORD
012F 208400 JSR SAVOP
0132 E8 INX
0133 E040 CPX #40
0135 DOF2 BNE NXT
0137 4CWOl JMP GTEST