|Contents||What's new ?|
|Schematics Microtan Java emulator||
Feel again the 1980' atmosphere : enter the 1k 6502 programming contest !
Please go to the 1K 6502 programming page and show your skill !!
65 is Oric-1's ancestor !
How's that beast ?
With the Oric-1, Tangerine's quest for a cheap design was clearly targeting Sinclair's market. Even if the form factor of the Microtan 65 has no resemblance with the ZX80, comparing the ancestors of the Spectrum and the Oric is interesting...
1 KB ram standard, including video memory ! This limitation really affects the Microtan, since the 6502 processor usually uses page 0 for variables, and page 1 for stack. On the Microtan, pages 2 and 3 are used as the video memory (16x32 chars). Where do you fit your code ?-) These tight constraints prevent the use of the BASIC language on the Microtan (BASIC65 uses a lot of page0 for its variables), so the un-extended Microtan was only usable in machine code. On the other side, the ZX80 had a way to dynamically extend the video memory (called video-file) from a minimum 25 bytes to a full 793 bytes. Anyway, the Microtan65 could grow up to a much bigger system: with the TANEX expansion board, 7 KB of static ram could be added, and you could add again 40KB of dynamic ram with the TANRAM board, for a total 48KB (and I've also read about the TANDISC board, which was allowing to read floppy disks with DMA).
1 KB rom standard ! This rom contained TANBUG v1, a monitor which allowed you to enter machine code programs. It was a rather primitive monitor indeed, but the hardware of the Microtan features an interrupting device which allows to single-step programs (even ROM based ones), and a button for interrupting mad programs, so you didn't have to retype your program for every bug. On the other hand, no facility was offered on the un-extended Microtan to save programs on tapes or anything else... you had to enter your programs from the keyboard every time, hopefully they couldn't be too big as said above. On the ZX80, thanks to a specially developed 4KB integer-Basic, you were able to fit bigger programs more easily. Once again, the Microtan was highly expandable, the 1K TANBUG rom (version 2 was 2KB) could be complemented with 14 KB rom on the TANEX board.
Simple video hardware, and semi hi-resolution ! No ULA yet, you can read how the video signal is generated from the schematics. With 16 lines of 32 great-looking characters (8x16 matrix), and exploiting a nice feature of the 6502 (the bus is idle during half of its clock period), the Microtan offered a flicker-free display. On the ZX80, the Z80 (assisted with simple hardware) was responsible for the video generation of the 24x32 character display (8x8 character matrix), so when you were running a program, there was no image on the monitor... Both computers have the capability to use graphics characters: the ZX80 matrix character can be divided by 4 thanks to 8 mosaic characters (and their video inverse), leading to a 64x48 resolution. On the Microtan65, the memory is in fact 1K x 9bit, this 9th bit being automatically added each time you write to memory (but you can't read it), and used by the video hardware to select on-the-fly generated mosaic characters (they aren't stored in a prom). 256 mosaic characters allows to divide the character matrix by 8, giving a 64x64 total resolution. Thanks to Ray Gannon who sent me the schematics, you can fully appreciate this video hardware...