[sdiy] Fwd: MIDI spec / implementation question

[The Old Crow]

On Fri, 30 Mar 2001, Frank Lemieux wrote:

> I decided that for my project in Signal Acquision class that I'd build
> a MIDI interface for our 8085 based class computer.  When browsing
> through an online copy of the spec, some questions have come up.
>
> 1. One reference states that MIDI is a 5mA current loop, and another
> states that it is 50mA.  Which is more correct?

  Five mA.

> 2.  I'm using an 82C51AC as UART, as it is what I'm familiar with.  Are 
> there any caveats to using this for MIDI?

  Now THIS takes me back...My CP/M system built in 1978 used two 8251
USARTs on an S-100 card.  RDA was bit 1 and TBE was bit 4 in the status
register.  Haven't used one in almost 20 years and I remember that,
sheesh.

  You should be able to use the 8251 just fine for MIDI, just remember it
has no hardware buffer beyond the receiver holding register.

> 3.  The best optocoupler I have available is an HCPL-2531.  Is there 
> anything I haven't thought of regarding its use?

  As long as it has a fast switching time, should be no problem.  I've
used H11A1's for MIDI, and they aren't exactly "spec".

Crow

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