19 Dec
2015
19 Dec
'15
12:54 a.m.
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.