Re: the slotlessness of sound cards

[Jeff Blakeney <CUTjblakeney@sentex.net>]

On Fri, 4 Apr 2003 00:52:56 -0500, "Bill Garber"
<willy46pa@comcast.net> wrote:

>Actually, MIDI is nothing more than serial. MIDI-IN is -Rxd + Gnd,
>MIDI-OUT is -Txd + Gnd.

It is a little more than that.  Standard serial communications use a
change in voltage level to indicate a change in binary state (one
voltage signifies a zero and another voltage signifies a one).  MIDI
on the other hand uses changes in current to indicate changes in
binary state.  This is why you need the MIDI box for the IIgs, to
convert the serial port's voltages to the currents needed by the MIDI
standard.  That box also optically isolates the IIgs from the MIDI bus
which is another requirement of the MIDI standard.

And to let anyone curious know why they can't use this MIDI box on
other models of Apple II, it is because the MIDI standard also uses a
weird transfer rate (31.5 kbps if I remember correctly) and the IIgs
serial controller can be set to this speed but other models of Apple
II can't (with the possible exception of the IIc+ but it doesn't have
a driver or any software that supports the box on that machine).

-- 
 Jeff Blakeney - Dean of the Apple II University in the
                 Apple II Community on Syndicomm.com
 CUT the obvious from my address if you want to e-mail me