PseudoDisk ][ and IIGS

["Alex Freed" <alexf@mirrow.com>]

A bit of bad news. I tested the PD on a IIGS and it doesn't work well.
Half the time it doesn't work at all. The other half I do get to my
selection
program prompt. Nibble images work after that but ProDOS mostly fails.

So I looked at the Apple IIGS TechNotes  #68 and found 2 things:

1. Recomendation to delay driving the data bus by 60 nS after the PH0.
For example by using LS TTL circuits that provide about that much delay.

My CPLD is pretty fast - 10 nS. So I'm clearly violating this condition.
To comply with the recommendation I would need to wire at least one extra
signal from the slot - 7M.

2. Apple also warns that
"Since the Apple II expansion slots were designed with only one ground pin,
complex expansion cards sometimes have problems with excessive ground
noise--
especially in the IIGS, where the signals typically have faster rise and
fall
times."

They suggest using a lot of capacitors on all unused power lines.


One or both of the above may be the reason for the flaky behaviour I've
observed.



-- 
-Alex.