Decoding MIDI with discrete logic

[Gene Zumchak]

Michael,

    The serial stream you want to read is self-clocking.  No clock is provided.
You really need a UART.  While you could use a discrete UART chip and other
discretes around it, it's going to cost a lot more and be a lot less versatile,
if you can get it to work, than a microcomputer approach.  You need to find a
buddy who does this kind of stuff to get  you started.  I have a few copies of my
out of print book Microcomputer Design & Troubleshooting that I'm will to part
with for $25 postpaid.  Some of the stuff in it is dated, but I think that it's a
good intro to Micro's and doing stuff with them.

Gene Z.



WeAreAs1 at aol.com wrote:

> Hello list,
>
> I have a need for a couple of boxes that will decode a simple MIDI message
> and output a high or low logic signal.  I have absolutely no software
> programming skills, so I cannot use a microprocessor or PIC device to do
> this, even though that might be the most efficient method.
>
> The MIDI message would be a continuous controller (the controller number is
> as yet to be determined - probably one of the less often used ones).  I want
> the logic gate output to go high, and stay high, whenever this particular
> controller is received with a value of 64 or higher.  If the decoder circuit
> receives that same controller with a value of 63 or lower, the logic output
> would then go low, and stay low.
>
> I am wondering about using discrete logic IC's to do the job, and I'd like to
> know if others have made similar attempts.  I haven't yet tried to work out
> the details on paper, but in my head I've figured out some rough ideas:
>
> I would clock the incoming serial MIDI data through a few cascaded
> serial-to-parallel shift register chips (74ls164 or similar), and send the
> 3-byte parallel output to a few "equality/magnitude comparator" chips
> (74ls686 or similar), one chip for each byte: Status/Channel, Controller
> Number, Value), to be compared with the specific preset MIDI byte that they
> need to respond to.  The first two comparators (looking at the Status/Channel
> and Controller Number bytes) would be in "Equality Comparator" mode, and
> their outputs would be AND'ed together to give a True output if they both
> exactly agreed with the preset bytes.  I would use "Magnitude Comparator"
> mode for the last byte (Controller Value) and would compare the incoming byte
> with a preset byte having a value of 63, so the magnitude comparator output
> would go True for any Value bytes greater than 63, and go False for any bytes
> valued 63 or lower.  The output of the third comparator would then be AND'ed
> with the output of the previously mentioned AND gate (the "True" signal from
> the correct Status and CC# bytes), and that would be my final output.
> Hopefully, the MIDI Stop Bits would allow the Serial-to-Parallel converters
> to keep track of the incoming MIDI bytes, and the comparators and associated
> logic would simply ignore all incoming MIDI messages except the important
> one.
>
> Obviously, I haven't completely thought this out, and there is probably a
> more elegant way to do this, but am I at all on the right track here?  Is
> there a simpler way to do this (without using a microprocessor)?  What are
> some traps that I must watch out for?  I've seen some circuits that use a
> UART chip, hard-wired with some external logic, to achieve a similar result,
> but I didn't really understand them (I couldn't find enough background
> material about the inner workings of the UART chips).  Has anyone done any
> non-microprocessor MIDI stuff with any of those types of devices?  (6502,
> AY-1013, AY-1015, etc.)  Do you know where I can find data sheets on them?
>
> If any of you have built MIDI devices using discrete logic, I'd love to see
> your circuits.  Even if their purpose or function is completely different
> than the one I have described, I'm sure that I would still learn something
> useful from them.
>
> Best regards,
> Michael Bacich
>
> P.S. - Yes, I know that MIDI Solutions makes a nice little box that will do
> what I need done, but that wouldn't be DIY, would it?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/19990430/7e245e93/attachment.htm>