WD900-FD-ADAPTER notes
2015-12-02

Copyright 2015 Eric Smith <spacewar@mail.com>

The WD900-FD-ADAPTER hardware design files, including the schematic
diagram, printed circuit board layout, and this README.txt file are
provided under the Creative Commons Attribution-ShareAlike 4.0
International license, which is in the file legalcode.txt or may be
found at:

	http://creativecommons.org/licenses/by-sa/4.0/

Description:

The Western Digital Pascal Microengine board (WD900) and box (WD90)
use a DC37S connector for attachment of external 8-inch floppy drives.
The WD900-FD-ADAPTER adapts the DC37S connector to a 50 pin shrouded
male header using the standard 8-inch floppy drive pinout.

The WD900 uses a WD FD1791 floppy disk controller chip. Typically the
HLD (Head Load) output of the FD1791 would drive a one-shot, and the
output of the one-shot would drive the FD1791 HLT (Head Load Timing)
input, with the one-shot adjusted to provide a time delay of at least
as long as the drive head load time. The WD900 wires HLT to a pin of
the DC37S connector. The WD900-FD-ADAPTER uses a PIC microcontroller
to provide head load timing with 16 time delays selectable by a
four-position DIP switch.


Revision 1 Design Errors:

* P5 pin 1 is on OPPOSITE row of connector from dot. The dot is
  actually nearest to P5 pin 2.

Possible improvements for a future revision:

* should have a power LED
* should have ground, power test points
* PIC pin 4 (MCLR) should have a pullup resistor. Not strictly
  necessary as long as config bits are set to disable MCLR.
* ICD 6-pin SIP connector should be rotated 180 degrees to be more
  suitable for use of a right-angle header
* Modular connector footprint should be added for ICD (stuff option:
  6-pin SIP, modular, none)
* need to select NAMES and VALUES layers for silkscreen