I want to build a Midi interface to attach to a SBC2 65c02 computer...I am looking to build a 65c02 and program it. I program Machine Language, but I don't know hardware as well, so I am puzzled at how to build a Midi interface. I know the midi spec inside and out I know logically how to program for the interface...I know it's like 32k bps or so, but I need hardware guidance.

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www.insanityvoid.com (My Music Recordings)
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Hi Ivlenk,

Here is a web-site with some midi stuff.

http://home.concepts-ict.nl/~nctnico/index.htm

Also visit this general engineering site that is very very good.
It has a midi section!

http://www.epanorama.net/index.php


Cheers,

Paul

This is tip #11 from my "Tip of the Day" posts on the older Delphi 6502 forum (which is still there so you can refer back to older 6502 discussions):
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The MIDI (musical instrument digital interface) bit rate is 31,250bps, which is not a standard rate option for the 6551 ACIA with a 1.8432 MHz crystal. To get it, set the 6551 for one-sixteenth of the XTAL clock input rate, and then feed it with 500kHz instead of 1.8432MHz. Get the 500kHz off of a 6522's PB7 from its free-running T1. If you have a 6522 put out a steady square wave on PB7 from T1, the frequency is: f=Ph2/(2(n+2)), where Ph2 is the phase-2 system clock frequency, and n is the T1 latch value.
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So if you have a 6551 ACIA and a 6522 VIA and use those:

Set VIA_DDRB<7> to make PB7 an output bit.
Set VIA_ACR<6,7> for free-running T1 output on PB7, no IRQ.
Store 3 in VIA_T1CL for 500kHz PB7 output if ph2 is 5MHz
(Store 0 if ph2 is 2MHz. Equation is above.)
Store 0 in VIA_T1CH (do this _after_ writing to T1CL above)

Feed the 500kHz from VIA PB7 into ACIA XTAL 1 input (DIP pin 6).
(Don't use a crystal with this ACIA.)
Don't connect ACIA RxC (DIP pin 5).

Store 0 in ACIA_STAT_REG for software reset.
Store 1011B in ACIA_COM_REG for no parity or echo, TX & RX enabled, no IRQ.
Store 10010000B in ACIA_CTRL_REG for 2 stop bits, 8 data, RX clock=TX clock,
and TX clock=1/16 of XTAL input freq.

Of course if you receive MIDI info too and not just transmit, you will definitely want interrupts; but when I fooled around with it, I only transmitted, which is one reason ACIA interrupts are shown disabled above. Since I only transmitted, I didn't have to put any optoisolators on the home-made computer side. I used only two wires, one from ACIA TxD through a 220-ohm resistor to pin 5 of a male 5-pin DIN connector, and another wire from +5V through a 220-ohm resistor to pin 4 of the same DIN. The DIN connector pins are numbered in a way you might not expect. As you look into the end of the male connector with the middle pin at the top, you have starting at 9 o'clock pin 3, going clockwise to 5, 2 (at 12 o'clock), 4, and finally pin 1 at 3 o'clock.

Garth
engr@drecomm.com

I remember building a MIDI interface for my VIC-20 back in the mid 80's. To keep the part count down, I used a 6551 with a 3Mhz crystal to get the 31,250 Hz needed.

Ray

Here is the math:

1843200 Crystal Hz / 19200 (baud setting 1111) = 96 (6551 internal divider)


31250 MIDI * 96 (6551 internal divider) = 3000000 Crystal Hz

Ray

Hi,

You can view all of the "Tip of the Day" posts in the Delphi archive:

http://www.6502.org/forum/topic/342

Regards,
Mike

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- Mike Naberezny (mike@naberezny.com) http://6502.org