The optical isolation is intended to eliminate any problems with the various
devices in the midi chain having different ground potentials.

Bob Ammerman
RAm Systems

----- Original Message -----
From: "iain duncan" <iainduncan@TELUS.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, August 23, 2004 6:45 AM
Subject: Re: multiple 4x4 keypads to 16f877 or 18f452?


> Bob Ammerman wrote:
> > MIDI in and out work fine on a traditional UART. The baud rate is 31
250,
> > which works out perfectly when using an crystal that is an exact number
of
> > MHz (as opposed to some funny number).
> >
> > However, rather than using conventional RS232 levels, proper MIDI uses
an
> > opto-isolated connection.
>
> Bob, what's the deal with the opto-isolation? I've noticed some examples
> on line have it, some don't. Do I *need* to include opto-isolation to
> just get simple output, or is there some other way? And why is
> necessary, ie why can't I just bring down the voltage level on the pins
> to acceptable midi range using diodes or what not? ( Am very much a
> beginner with electornics. I am more scared of external chips than I am
> of bit banging serial i/o myself, ha ha. )
>
> Iain
>
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