How to build a MIDI interface for the Commodore 64
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 serviceable.
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 acceptable 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 16 15 15
Enable Xmit/Rcv + Rcv Interrupt 96 95 95
Enable Xmit/Rcv + Xmit Interrupt 36 35 35
Enable Xmit/Rcv + Both Interrupts B6 B5 B5
One final note: any software package which uses the "smart" features of a specific interface (i.e. it's on-board clock(s), tape/drum sync, foot switch interfaces, etc.) will probably not work unmodified with this simple MIDI (UART only) interface. However, a vast majority of public-domain S/W will work fine as long as the standard supported is one of the 3 above and the hardware and software standards match. Also beware that the Siel/JMS standard (also DATEL) is the LEAST likely to be supported by software in the U.S. (Passport is perhaps the MOST supported, with Sequential running a close second).
Sincerely,
Frank Prindle
Prindle@NADC.arpa
--------------------- Cut Here - PostScript document follows ------------------
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% Polyline
newpath 134 699 moveto 174 699 lineto stroke
% Polyline
newpath 134 679 moveto 174 679 lineto stroke
% Polyline
newpath 64 719 moveto 134 719 lineto stroke
% Polyline
newpath 69 714 moveto 64 719 lineto 69 724 lineto stroke
% Polyline
newpath 94 719 moveto 94 694 lineto stroke
% Polyline
newpath 94 694 moveto 99 689 lineto stroke
% Polyline
newpath 94 694 moveto 89 689 lineto stroke
% Polyline
newpath 174 469 moveto 174 729 lineto stroke
% Polyline
newpath 564 764 moveto 584 764 lineto stroke
% Polyline
newpath 568 768 moveto 580 768 lineto stroke
% Polyline
newpath 572 772 moveto 577 772 lineto stroke
% Polyline
newpath 479 704 moveto 479 744 lineto stroke
% Polyline
newpath 479 744 moveto 579 744 lineto 579 704 lineto 479 704 lineto stroke
% Polyline
newpath 489 704 moveto 489 689 lineto stroke
% Polyline
newpath 494 684 moveto 489 689 lineto 484 684 lineto stroke
% Polyline
newpath 369 744 moveto 369 754 lineto 574 754 lineto 574 744 lineto stroke
% Polyline
newpath 429 744 moveto 429 754 lineto stroke
% Polyline
newpath 454 744 moveto 454 754 lineto stroke
% Polyline
newpath 489 744 moveto 489 754 lineto stroke
% Polyline
newpath 549 744 moveto 549 754 lineto stroke
% Polyline
newpath 574 754 moveto 574 764 lineto stroke
% Polyline
newpath 359 704 moveto 359 744 lineto 459 744 lineto 459 704 lineto 364 704 lineto stroke
% Polyline
newpath 359 704 moveto 374 704 lineto stroke
% Polyline
newpath 369 704 moveto 369 689 lineto stroke
% Polyline
newpath 369 689 moveto 374 684 lineto stroke
% Polyline
newpath 369 689 moveto 364 684 lineto stroke
/Courier-Bold findfont 13.333333 scalefont setfont
499 304 moveto 1 -1 scale (O2 \(Pin E\)) show 1 -1 scale
420 471 moveto 1 -1 scale (Vss) show 1 -1 scale
19 499 moveto 1 -1 scale (\(Pin S\)) show 1 -1 scale
99 254 moveto 1 -1 scale (N/C) show 1 -1 scale
104 144 moveto 1 -1 scale (560pf) show 1 -1 scale
434 94 moveto 1 -1 scale (13) show 1 -1 scale
204 644 moveto 1 -1 scale (7) show 1 -1 scale
59 789 moveto 1 -1 scale (indicates a pin on the 16-pin personality select DIP socket.) show 1 -1 scale
34 279 moveto 1 -1 scale (Jack) show 1 -1 scale
34 264 moveto 1 -1 scale (DIN) show 1 -1 scale
34 249 moveto 1 -1 scale (IN) show 1 -1 scale
224 734 moveto 1 -1 scale (\(1/6\)74LS366) show 1 -1 scale
209 719 moveto 1 -1 scale (All inverters are) show 1 -1 scale
289 414 moveto 1 -1 scale (CS0) show 1 -1 scale
34 399 moveto 1 -1 scale (Jack) show 1 -1 scale
34 384 moveto 1 -1 scale (DIN) show 1 -1 scale
34 369 moveto 1 -1 scale (OUT) show 1 -1 scale
399 224 moveto 1 -1 scale (7) show 1 -1 scale
389 544 moveto 1 -1 scale (S) show 1 -1 scale
389 529 moveto 1 -1 scale (T) show 1 -1 scale
389 514 moveto 1 -1 scale (C) show 1 -1 scale
369 544 moveto 1 -1 scale (D) show 1 -1 scale
369 529 moveto 1 -1 scale (C) show 1 -1 scale
369 514 moveto 1 -1 scale (D) show 1 -1 scale
349 544 moveto 1 -1 scale (S) show 1 -1 scale
349 529 moveto 1 -1 scale (T) show 1 -1 scale
349 514 moveto 1 -1 scale (R) show 1 -1 scale
279 369 moveto 1 -1 scale (DATA) show 1 -1 scale
289 354 moveto 1 -1 scale (Tx) show 1 -1 scale
279 249 moveto 1 -1 scale (DATA) show 1 -1 scale
289 234 moveto 1 -1 scale (Rx) show 1 -1 scale
304 499 moveto 1 -1 scale (CS2) show 1 -1 scale
269 524 moveto 1 -1 scale (11) show 1 -1 scale
274 474 moveto 1 -1 scale (4) show 1 -1 scale
324 474 moveto 1 -1 scale (9) show 1 -1 scale
349 474 moveto 1 -1 scale (5) show 1 -1 scale
364 474 moveto 1 -1 scale (23) show 1 -1 scale
384 474 moveto 1 -1 scale (24) show 1 -1 scale
404 464 moveto 1 -1 scale (1) show 1 -1 scale
349 319 moveto 1 -1 scale (ACIA) show 1 -1 scale
349 304 moveto 1 -1 scale (6850) show 1 -1 scale
379 174 moveto 1 -1 scale (Vcc) show 1 -1 scale
319 424 moveto 1 -1 scale (8) show 1 -1 scale
499 284 moveto 1 -1 scale (12) show 1 -1 scale
499 244 moveto 1 -1 scale (14) show 1 -1 scale
499 264 moveto 1 -1 scale (A0 \(Pin Y\)) show 1 -1 scale
499 224 moveto 1 -1 scale (IRQ \(Pin 4\)) show 1 -1 scale
434 444 moveto 1 -1 scale (D0) show 1 -1 scale
434 429 moveto 1 -1 scale (D1) show 1 -1 scale
434 414 moveto 1 -1 scale (D2) show 1 -1 scale
434 399 moveto 1 -1 scale (D3) show 1 -1 scale
434 384 moveto 1 -1 scale (D4) show 1 -1 scale
434 369 moveto 1 -1 scale (D5) show 1 -1 scale
434 354 moveto 1 -1 scale (D6) show 1 -1 scale
434 339 moveto 1 -1 scale (D7) show 1 -1 scale
434 304 moveto 1 -1 scale (E) show 1 -1 scale
434 284 moveto 1 -1 scale (R/W) show 1 -1 scale
434 264 moveto 1 -1 scale (RS) show 1 -1 scale
434 244 moveto 1 -1 scale (CS1) show 1 -1 scale
434 224 moveto 1 -1 scale (IRQ) show 1 -1 scale
394 304 moveto 1 -1 scale (14) show 1 -1 scale
394 284 moveto 1 -1 scale (13) show 1 -1 scale
394 264 moveto 1 -1 scale (11) show 1 -1 scale
394 244 moveto 1 -1 scale (10) show 1 -1 scale
394 444 moveto 1 -1 scale (22) show 1 -1 scale
394 429 moveto 1 -1 scale (21) show 1 -1 scale
394 414 moveto 1 -1 scale (20) show 1 -1 scale
394 399 moveto 1 -1 scale (19) show 1 -1 scale
394 384 moveto 1 -1 scale (18) show 1 -1 scale
394 369 moveto 1 -1 scale (17) show 1 -1 scale
394 354 moveto 1 -1 scale (16) show 1 -1 scale
394 339 moveto 1 -1 scale (15) show 1 -1 scale
319 344 moveto 1 -1 scale (6) show 1 -1 scale
184 404 moveto 1 -1 scale (+5V) show 1 -1 scale
129 239 moveto 1 -1 scale (diode) show 1 -1 scale
129 299 moveto 1 -1 scale (220) show 1 -1 scale
129 419 moveto 1 -1 scale (220) show 1 -1 scale
129 329 moveto 1 -1 scale (220) show 1 -1 scale
84 394 moveto 1 -1 scale (4) show 1 -1 scale
84 364 moveto 1 -1 scale (2) show 1 -1 scale
84 334 moveto 1 -1 scale (5) show 1 -1 scale
34 354 moveto 1 -1 scale (MIDI-) show 1 -1 scale
199 284 moveto 1 -1 scale (1) show 1 -1 scale
199 224 moveto 1 -1 scale (2) show 1 -1 scale
84 274 moveto 1 -1 scale (4) show 1 -1 scale
84 244 moveto 1 -1 scale (2) show 1 -1 scale
84 214 moveto 1 -1 scale (5) show 1 -1 scale
34 234 moveto 1 -1 scale (MIDI-) show 1 -1 scale
244 284 moveto 1 -1 scale (5) show 1 -1 scale
244 224 moveto 1 -1 scale (4) show 1 -1 scale
219 214 moveto 1 -1 scale (6) show 1 -1 scale
144 184 moveto 1 -1 scale (+5V) show 1 -1 scale
244 169 moveto 1 -1 scale (270) show 1 -1 scale
204 254 moveto 1 -1 scale (PC900) show 1 -1 scale
319 224 moveto 1 -1 scale (2) show 1 -1 scale
464 164 moveto 1 -1 scale (+5V) show 1 -1 scale
394 194 moveto 1 -1 scale (12) show 1 -1 scale
359 194 moveto 1 -1 scale (4) show 1 -1 scale
319 194 moveto 1 -1 scale (3) show 1 -1 scale
339 174 moveto 1 -1 scale (CLK) show 1 -1 scale
344 159 moveto 1 -1 scale (Tx) show 1 -1 scale
299 174 moveto 1 -1 scale (CLK) show 1 -1 scale
304 159 moveto 1 -1 scale (Rx) show 1 -1 scale
354 109 moveto 1 -1 scale (16) show 1 -1 scale
319 109 moveto 1 -1 scale (1) show 1 -1 scale
274 109 moveto 1 -1 scale (15) show 1 -1 scale
59 69 moveto 1 -1 scale (2.2K) show 1 -1 scale
134 34 moveto 1 -1 scale (2Mhz.) show 1 -1 scale
154 69 moveto 1 -1 scale (2.2K) show 1 -1 scale
389 64 moveto 1 -1 scale (11) show 1 -1 scale
484 64 moveto 1 -1 scale (14) show 1 -1 scale
399 94 moveto 1 -1 scale (4) show 1 -1 scale
459 94 moveto 1 -1 scale (12) show 1 -1 scale
484 94 moveto 1 -1 scale (7) show 1 -1 scale
414 49 moveto 1 -1 scale (74LS293) show 1 -1 scale
554 64 moveto 1 -1 scale (+5V) show 1 -1 scale
499 339 moveto 1 -1 scale (D7 \(Pin 14\)) show 1 -1 scale
499 354 moveto 1 -1 scale (D6 \(Pin 15\)) show 1 -1 scale
499 369 moveto 1 -1 scale (D5 \(Pin 16\)) show 1 -1 scale
499 384 moveto 1 -1 scale (D4 \(Pin 17\)) show 1 -1 scale
499 399 moveto 1 -1 scale (D3 \(Pin 18\)) show 1 -1 scale
499 414 moveto 1 -1 scale (D2 \(Pin 19\)) show 1 -1 scale
499 429 moveto 1 -1 scale (D1 \(Pin 20\)) show 1 -1 scale
499 444 moveto 1 -1 scale (D0 \(Pin 21\)) show 1 -1 scale
274 644 moveto 1 -1 scale (7) show 1 -1 scale
274 624 moveto 1 -1 scale (5) show 1 -1 scale
274 604 moveto 1 -1 scale (3) show 1 -1 scale
274 584 moveto 1 -1 scale (2) show 1 -1 scale
499 644 moveto 1 -1 scale (GND \(Pin 1\)) show 1 -1 scale
499 624 moveto 1 -1 scale (R/W \(Pin 5\)) show 1 -1 scale
499 604 moveto 1 -1 scale (A3 \(Pin V\)) show 1 -1 scale
499 584 moveto 1 -1 scale (A2 \(Pin W\)) show 1 -1 scale
499 564 moveto 1 -1 scale (A1 \(Pin X\)) show 1 -1 scale
274 564 moveto 1 -1 scale (6) show 1 -1 scale
39 484 moveto 1 -1 scale (A6) show 1 -1 scale
39 524 moveto 1 -1 scale (A5) show 1 -1 scale
19 539 moveto 1 -1 scale (\(Pin T\)) show 1 -1 scale
39 564 moveto 1 -1 scale (A4) show 1 -1 scale
19 579 moveto 1 -1 scale (\(Pin U\)) show 1 -1 scale
44 604 moveto 1 -1 scale (13) show 1 -1 scale
34 644 moveto 1 -1 scale (IO1) show 1 -1 scale
19 659 moveto 1 -1 scale (\(Pin 7\)) show 1 -1 scale
179 564 moveto 1 -1 scale (3) show 1 -1 scale
179 604 moveto 1 -1 scale (12) show 1 -1 scale
179 644 moveto 1 -1 scale (11) show 1 -1 scale
224 604 moveto 1 -1 scale (8) show 1 -1 scale
179 484 moveto 1 -1 scale (2) show 1 -1 scale
179 524 moveto 1 -1 scale (1) show 1 -1 scale
199 499 moveto 1 -1 scale (+5V) show 1 -1 scale
34 724 moveto 1 -1 scale (+5V) show 1 -1 scale
19 739 moveto 1 -1 scale (\(Pin 2\)) show 1 -1 scale
79 684 moveto 1 -1 scale (+5V) show 1 -1 scale
179 684 moveto 1 -1 scale (4) show 1 -1 scale
179 704 moveto 1 -1 scale (5) show 1 -1 scale
179 724 moveto 1 -1 scale (6) show 1 -1 scale
179 584 moveto 1 -1 scale (74LS30) show 1 -1 scale
199 564 moveto 1 -1 scale (14) show 1 -1 scale
354 679 moveto 1 -1 scale (+5V) show 1 -1 scale
474 679 moveto 1 -1 scale (+5V) show 1 -1 scale
364 719 moveto 1 -1 scale (16) show 1 -1 scale
484 719 moveto 1 -1 scale (16) show 1 -1 scale
364 739 moveto 1 -1 scale (1) show 1 -1 scale
484 739 moveto 1 -1 scale (1) show 1 -1 scale
449 739 moveto 1 -1 scale (8) show 1 -1 scale
419 739 moveto 1 -1 scale (15) show 1 -1 scale
539 739 moveto 1 -1 scale (15) show 1 -1 scale
569 739 moveto 1 -1 scale (8) show 1 -1 scale
389 724 moveto 1 -1 scale (74LS366) show 1 -1 scale
509 724 moveto 1 -1 scale (74LS366) show 1 -1 scale
showpage
$F2psEnd
