Notes: --------- - the figures are in PDF format (Portable Definition File), you need the Acrobat Reader to view them (this program is available for a wide range of platforms). The document is two pages long. - figures don't show Vcc and Vss lines, be sure to connect those +5V and GND pins as described in the connections below. - only A7 is missing in the decoding stage, this means the interface is accessible in both 031C-031F and 039C-039F ranges - you don't need the MAX232 circuit if you only want a TTL interface (e.g: connecting to a minitel) - no +12/-12 needed, the MAX232 chip provides EIA compatible levels (9V) - as the MAX232 chip only allows two inputs and two outputs, I had to choose one input among DCD, DSR and CTS; and one output among DTR and RTS. DCD seems to be the most important input if you connect a modem to the interface (it tells you when you are connected), that's why I choose it. Also, I have chosen DTR rather than RTS in order to tell the attached equipment when the cpu is ready, and this signal is usually connected to both DSR and DCD in a null-modem cable. If you want all the modem lines, there's a MAX233 with more converters, I will surely update this add-on with it soon... - RxC may be connected to 02 (Phi2) divided by 2 in order to provide 31250 baud rate (standard for MIDI, but you need a voltage/current interface), or to the 1.8432 MHz clock in order to get 115200 baud speed. Connections: ------------ 74LS138: -------- 1. A to A2 16. Vcc 2. B to A3 15. Y0 nc 3. C to A5 14. Y1 nc 4. G2A to A6 13. Y2 nc 5. G2B to -I/O 12. Y3 to -CS1 (ACIA) 6. G1 to A4 11. Y4 nc 7. Y7 nc 10. Y5 nc 8. GND 9. Y6 nc 74LS09: ------- 1. 1A to -IRQ (ACIA) 14. Vcc 2. 1B to +5V 13. nc 3. 1Y to -IRQ (exp. port) 12. nc 4. 2A to Y3 (LS138) 11. nc 5. 2B to +5V 10. nc 6. 2Y to -I/OCTRL 9. nc 7. GND 8. nc ACIA 6551: ---------- 1. GND 28. R/-W to R/-W (exp. port) 2. CS0 to +5V 27. 02 to 02 (exp. port) 3. -CS1 to Y3 (LS138) 26. -IRQ to 1A (LS09) 4. -RES to -RST (exp. port) 25. DB7 to D7 5. RxC nc 24. DB6 to D6 6. XTAL1 to cristal 23. DB5 to D5 7. XTAL2 to cristal 22. DB4 to D4 8. -RTS nc 21. DB3 to D3 9. -CTS to ground 20. DB2 to D2 10. TxD to MAX232 19. DB1 to D1 11. -DTR to MAX232 18. DB0 to D0 12. RxD to MAX232 17. -DSR to ground 13. RS0 to A0 16. -DCD to MAX232 14. RS1 to A1 15. Vcc to +5V