[sdiy] MIDI specifications

[patchell]

    The problem I have seen with Midi Thru's is not so much the delay, but
rather the distortion to the wave form caused by the opto coupler.  The rise
and fall times through the opto coupler are not equal.  When you feed a
waveform into it is, in the simple case, a 50% square wave, you do not get a
50% square wave coming out.  After you go through a few of these, the poor
Uart in the midi device is going to have a hard time trying to figure out what
is is you are trying to tell it.

Paul Maddox wrote:

> Robert,
>
> > Isn't the logic delay time shorter than one microsecond?  Good old TTL
> > would run at 10-20 Mhz.  Wouldn't that imply that logic delay time would
> be
> > quite a bit shorter than one microsecond?
>
> yes, but you're going through a OPTO-Isolator, a logic gate, and a
> trasnsistor (or second logic gate)..
> so its not just the TTL logic...
> Do this 2 or three times, and you're delay is noticable.
> Especially at high tempos.
>
> Paul

--
 -Jim
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