The following text is a construction article for building your own MIDI interface for the Commodore 64 or Commodore 128 cartridge port. If you are used to building digital electronic projects, you should be able to put one together in a few days for about $25 worth of parts. However, this is not a project for the inexperienced - wiring this circuitry onto a board small enough to fit into a cartridge case requires a good eye, a steady hand, and a lot of patience. If you don't even know what a MIDI interface is, it means Musical Instrument Digital Interface, and is used to communicate with MIDI capable musical instruments. MIDI is an electronic music industry standard. The C64 was one of the first computers to be used extensively for MIDI applications. Don't even think of downloading this file to your C64, there is absolutely no reason to do so, since it is just a text file that you can print on your local host, and besides it contains lots of characters that aren't even on some Commodore compatible printers. When you print this out, make sure you allow a full 66 lines per printer page in order to fit the schematic on one page by itself. Following the construction article is a PostScript program which you can send to an Apple Laser Writer (or any PostScript compatible printer) to get a really high quality printout of the construction schematic. But don't fret if you don't have access to one of these - the ASCII version of the schematic below is quite servicable. If you do build this MIDI interface, or simply buy one, be sure to look for my package "The MIDI-SID CONNECTION", to be uploaded to the UXMAZE server soon. I will also entertain the idea of uploading other public domain MIDI software if there is enough interest. Just let me know. Sincerely, Frank Prindle Prindle@NADC.navy.mil ----------------------------------cut here------------------------------------- ____ COMMODORE 64 TRI-STANDARD MIDI INTERFACE |xtal| .----------. *----------|-||-|----------* *------------------|11 14|----<+5V | 2Mhz|____| | | | 74LS293 | | | | *--|4 12 7|----* *--\/\/\--* *--\/\/\--* | | '----------' | | 2.2K | | 2.2K | | 15 1 | | | | |\ | | |\ | |\ *-----@ @ @ *---------* | | \ | || | | \ | | \ | | 16 | *--| >o--*--||--*--| >o--*--| >o--* *----* V | / 500pf|| | / | / | | *---<+5V GND |/ |/ |/ Rx| Tx| | CLK| CLK| Vcc| +5V>-----*----\/\/\---* .--------------. | 270 | | 3 4 12 | ___ ___ MIDI-IN DIN Jack .-------. | | 7|-IRQ--->IRQ (Pin 4) 5<>--------------*--|2 6 | | | | | | 4|--------*--Rx-|2 10|-CS1------------@14 2<>--N/C diode V | PC- | DATA| | --- | 900 | | 11|-RS---->A0 (Pin Y) 220 | | 5|------* | | _ 4<>-------\/\/\--*--|1 | | | 13|-R/W------------@12 '-------' V | 6850 | GND | ACIA 14|-E----->02 (Pin E) /| /| | | MIDI-OUT DIN Jack / | / | | 15|-D7---->D7 (Pin 14) 5<>----\/\/\------o< |----o< |--------Tx-|6 16|-D6---->D6 (Pin 15) 220 \ | \ | DATA| 17|-D5---->D5 (Pin 16) 2<>---* \| \| | 18|-D4---->D4 (Pin 17) | | 19|-D3---->D3 (Pin 18) V | 20|-D2---->D2 (Pin 19) GND 220 |\ | 21|-D1---->D1 (Pin 20) 4<>-------\/\/\---<+5V | \ | 22|-D0---->D0 (Pin 21) *---| >o-*-CS0-|8 | | | / | | 9 5 1 23 24| |\ | |/ | '--------------' | \ | | @ | | | | | A6 <----| >o-----------|2 | 4 @---* *-*-*--*-------* (Pin S) | / | | 11 ___ _ _ ___ | |/ |\ | | CS2 R V D CTS V | \ | | T s C GND A5 <---------| >o------|1 | S s D (Pin T) | / | | |\ |/ | *-----* | \ |--_ | 6@------->A1 (Pin X) A4 <----| >o-----------|3 \ | (Pin U) | / | 74 \ 8 | 2@------->A2 (Pin W) |/ |\ |LS30 |o--* | \ | / 3@------->A3 (Pin V) @-----------| >o------|12 / _ 13 | / |--- 5@------->R/W (Pin 5) |\ |/ | ___ | \ | IO1<----| >o-----------|11 NOTES: (Pin 7) | / | 1. All inverter/buffers are (1/6)74LS366 |/ +5V | with pins 1, 8, and 15 grounded; pin ^ *---|4 16 supplied with +5V. 2 chips needed. | | | 2. A .01 uf bypass capacitor from Vcc to +5V<---------*------*---|5 GND at each chip is not a bad idea. (Pin 2) | | 3. The PC900 optoisolator available from *---|6 MIX Bookshelf, 6400 Hollis St. #12, 7 GND | | Emeryville, CA 94608; price $3.00 PP. @ ^ *---|14(Vcc) 4. All (Pin #) numbers refer to the C64 | | | cartridge port connector CN6. GND<----*----*----------|7 (GND) 5. All @ symbol numbers refer to pins on (Pin 1) | a 16-pin personality select socket. This interface must be configured for a particular standard by plugging jumpers (or a jumpered DIP header) into the personality socket. The jumpers required for each standard are as follows: Passport Standard Sequential Standard Siel/JMS Standard ----------------- ------------------- ----------------- 1 - 16 1 - 16 1 - 15 3 - 14 4 - 14 2 - 14 2 - 13 3 - 13 3 - 13 5 - 12 6 - 12 6 - 12 6 - 11 2 - 11 7 - 11 To add a MIDI-THRU output jack, it will be necessary to add another 74LS366 chip, since two more inverters are required. Simply connect the output from pin 4 of the PC900 optoisolator to the following circuit in addition to pin 2 of the 6850: /| /| MIDI-THRU DIN Jack / | / | 5<>----\/\/\------o< |----o< |--------- from pin 4 of PC900 220 \ | \ | 2<>---* \| \| | V GND 220 4<>-------\/\/\---<+5V A 6N138 optoisolator is the only acceptable substitute for the PC900. It is available from retail parts distributors such as Active Electronics. Its pin- out is different: PC900 Pin Corresponding 6N138 Pin 1 2 2 3 4 6 5 5 6 8 Radio-Shack optoisolators are not an acceptible substitute! Resist the temptation to ground the outer shell contact of any DIN jack, or pin 2 of the MIDI-IN DIN jack. Doing so violates the MIDI standard and can cause all sorts of ground-loop problems depending on the cables used. The MIDI interface sold by DATEL has this flaw. Please consult the Motorola MC6850 Data Sheets for details on programming the 6850. As you can see, all three interface standards are very similar. The differences are in the frequency of the 6850 clock and the addressing of the 6850 registers. These differences are summarized in the following table: Siel/JMS Passport Sequential Control Register Address DE04 DE08 DE00 Transmit Data Register Address DE05 DE09 DE01 Status Register Address DE06 DE08 DE02 Receive Data Register Address DE07 DE09 DE03 Master Chip Reset Command 03 03 03 Enable Xmit/Rcv Command ...
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