Hi,

My last pic project was a midi switching device that would receive Program
Change information and recall via internal EEPROM data for that particular
change and display a three digit number and 8 leds ( It also scanned a
12-key keyboard and latched and external 74HC564.)

It was designed around a 16c84, but it was running at 8 Mhz. I used the
porta RTCC/RA4 pin configured as counter set to increment on falling edge
of external counter( the midi start bit ) loaded with FF as to cause an
interupt on overflow. From there its a matter of setting the RTCC back to
internal clock and waiting exactly until the middle of the next bit. Or you
could poll it a bunch of times and average the result. ( but not after the
initial start bit, too much going on!) Also, the interupts are disabled
during most of the midi byte.

The timing was very critical, even at 8 Mhz, and there was just barely
enough time even with 64 cycles! I couldn't emagine trying to squeeze it
down any further for this type of setup. You could maybe just poll a pin
like mad and reset a timer as soon as the start bit comes in.
Hope this helps.

p.s Watchout for AN555( Asychronous Serial I/O )!!! The code is sloppy,
indeed.
There are whole sections of code that do absolutely nothing! :-( Except
take the place of NOP's ;-)
Overall the Book is great, and I suggest getting it :-)

p.s ( I accidentaly sent this to Mike Watson, sorry mike )

Regards,
Hamilton

|_  _  _ _
| )(_|( | ) @  s l i p . n e t
h: http://www.slip.net/~ham
w: http://www.mesaboogie.com


At 08:52 AM 1/28/97 GMT, you wrote:
>In message  <32EDBFD6.7E32@isy.liu.se> PICLIST@MITVMA.MIT.EDU writes:
>> Craig Knotts wrote:
>> >
>> >      32 instructions isn't much in the way of elbow room... I'm having a
>> >      hard time imagining what you could usefully do with any MIDI data in
>> >      that amount of time.  Maybe at 10 MHz things would be easier.
>> >
>> >      Is this device a receive only, transmit only, or both?  I'd
certainly
>> >      wish for a built-in serial port before tackling MIDI for anything
but
>> >      the most simple task.
>>
>> Well, I'm not planning to do much processing, just receiving three bytes
in a
>> sequence, and then set/reset a bit or send out the data on the ports and go
>> back to receiving again. What do you think?
>>
>
>I think you will loose data if you wait for your transmission
>to end before you start receiving again.
>
>If I were to do it (and I have a project in mind) I would look
>to either bit-bang with a much higher clock speed (20MHz on a
>16C61) or go to one of the 28 pin pics with a uart on board.
>
>Regards,
>
>
>Mike Watson
>
>