Re: the slotlessness of sound cards

["Bill Garber" <willy46pa@comcast.net>]

> >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).

Taken from a thread on MIDI and serial:

MIDI is a serial communication stream running at the bizarre rate of 31250
baud.  I have to wonder if Sequential Circuits and the rest of the synth
companies at that point did this just to make MIDI different from computer
serial communications.  Unfortunately this baud rate was as badly conceived
as most of the MIDI 1.0 standard.  Standard computer serial interfaces have
no way of creating this goofy 31250 baud rate.  So, when you put your S80
"To Host" serial port into PC2 mode, all you are doing is sending and
receiving MIDI at 38400 baud over a serial cable.  This baud rate is native
to all standard serial cards.  It's about 20% faster than MIDI so
technically downloading over the serial cable is 20% faster than through
MIDI, but that's about it.

Product description: MIDI to serial
MIDI to SERIAL RS-232 converter

The UNWINDER can act as a MIDI-serial adapter, converting the Midi to
RS-232 for connection to a standard serial port.  Most SGI serial ports can
be set up as Midi ports communicating at 31250 baud.

There is plenty more where these came from. Please I used MIDI thru serial
port when it only ran at 15,600.

Bill @ GarberStreet Enterprises
http://garberstreet.netfirms.com



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