Article 4783 of comp.sys.atari.8bit: From: terpin@acsu.buffalo.edu (christophe d terpin) Newsgroups: comp.sys.atari.8bit Subject: Homemade MIDI Interface -- Part 1 of 2 Summary: How to build midi interface for Atari 8bit Keywords: MIDI, interface Date: 28 Mar 91 02:51:18 GMT Sender: news@acsu.Buffalo.EDU Organization: SUNY Buffalo Homemade MIDI interface for the Atari 8-Bit ------------------------------------------- Parts List: 1 7404 TTL Hex Inverter OR 7400 NAND gate 2 220 ohm resistors (10%) 1 Atari serial port plug for your computer 2 5-pin Midi plugs (RCA) for your midi keyboard 1 breadboard/experimenter perf board 1 project case approx. 10 ft. of 3 wire cable twist ties to tie down wires etc.. The serial port pins as seen on the computer are: 2 4 6 8 10 12 o o o o o o o o o o o o o 1 3 5 7 9 11 13 1 - Clock In 7 - Command 2 - Clock Out 8 - Motor Control 3 - Data In 9 - Proceed 4 - Ground 10 - +5V 5 - Data Out 11 - Audio In 6 - Ground 12 - +12V 13 - Interrupt For this project, we will only need to use pin #'s 3,4,5, and 10 of the serial port. --------------- (CRUDE) Ground (pin 4) SCHEMATIC: 7404 | |\ |\ 2| | \ | \ 220 ohm 5 o 4 data out ---| O--| O---\/\/\/---------o o---/\/\/\/-- +5 (pin 10) from computer | / | / 3 o o 1 (pin 5) |/ |/ MIDI OUTPUT cable to synth 2 5 o 4 Ground---o o------------(optoisolator)------- data in to computer 3 o o 1 (pin 3) MIDI INPUT cable from synth Pins 1,3 of the Midi Output cable and pins 1,2,3 of the Midi Input cable are not connected. The optoisolator is optional, although it is recommended for extra protection for your midi keyboard. I have used the interface hard wired without the optoisolator without any problems (so far). Also note: the normal serial i/o to the disk will sometimes interfere with the midi interface and vice versa. This sometimes results in a note sounding on the synth when loading or saving a file, or the disk will glitch if you try playing the keyboard during disk i/o. One possible way to remedy this annoying problem is to replace the 7404 with a tri-state buffer which can be turned to a high-Z state using the motor control (pin 8) from the serial port. Anyway, BE CAREFUL and check all your wiring before you hook the interface up to the synthesizer. Please let me know if you have any suggestions for improving the interface. next:: BASIC Midi Recorder Program New & Improved Assembly Source Code --------------------------------------------------------------- Christopher Terpin terpin@autarch.acsu.buffalo.edu