Description for CS/A SHUGART board, version 1.0
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whatsit	: PC-style Floppy interface (shugart-bus), 8 bit parallel port w/ handshake
I/O	: WD1772 at $8e0-$8ef, 6522 VIA at $8f0-$8ff
Mem	: --

IC1 determines a 32 byte I/O space area. Feeding A4 to the VIA's CS1 makes
it listen to $8f*. For the WD1770 Phi2 must be put into the chip select
signal, as there is no further timing input.

The WD1772 device-side handling is almost by the book. The only thing is
that I decided to use the PC-style MOTOR-ON handling, with two possible
drives with separate MOTOR-ON, instead of 4 possible drives with only
one common MOTOR-ON. 

One thing that is definitely _not_ by the book is the clock circuitry.
The WD1772 is only specified for 8 MHz input CLK. With the VIA PA5 I can
switch the input CLK to 16 MHz, which is outside the specs!
(IC7 divides the 16MHz clock by 2, giving the standard 8 MHz. the four
NAND gates from IC6 switch between these two clocks)
For me it works for using HD disks, but it may not for you, you are
warned!

The rest of the VIA (i.e. port B) is used to provide an 8-bit parallel
I/O port.