WD9000 Pascal Microengine floppy adapter (was Re: WD9000 Pascal microengine schematics available)

[Eric Smith]

On Wed, Nov 18, 2015 at 2:48 AM, Eric Smith <spacewar at gmail.com> wrote:
> I've designed a simple adapter PCB
[for the DC37S floppy connector of the Western Digital WD900/WD9000
Pascal Microengine]
> To support proper head load or motor spinup timing, I put an optional
> PIC microcontroller and DIP switch on the adapter, to act as a digital
> delay between HLD and HLT, with sixteen switch-selectable delays.

I've got the PIC code written and tested (standalone).

I saw some really weird behavior at first. There's a 10K SIP resistor
network for pullups, and I'd installed it backwards, so there was 20K
between logic signals instead of 10K between each and the +5V
low-impedance power rail. Since some of those logic signals were
intended to be driven by open-collector drivers, and weren't being
drive, it looked like the PIC was mysteriously driving some pins
configured as inputs. Once I figured that out and fixed it, the code
worked fine.