searching for replacement for 1793 FDC

[Michael Holley]

I did the FDC design using the WD2797 chip. Anyone can reuse the design as 
they wish. I have sold out of my original run of these boards.
http://www.swtpc.com/mholley/DC_5/DC5_Index.htm

The WD2797 has three adjustment, a capacitor and 2 trim pots.  I used a 
scope for these adjustment but then made a counter circuit  in the Xilinx 
CPLD to measure the pulse width. The adjustment procedure is given in the 
users guide.
http://www.swtpc.com/mholley/DC_5/DC5_DesignDescription.pdf

The circuit is in the design description.
http://www.swtpc.com/mholley/DC_5/DC5_DesignDescription.pdf

Working with the Xilinx XC9500 series CPLD is easy and they are 5 volt parts 
that you can get in PLCC packages. (Through hole sockets.)

Programming them takes a simple parallel port adapter that you can make on a 
small perf board. I have a small PCB and all of the parts I anyone wants to 
try to use them.
http://www.swtpc.com/mholley/DC_5/Cable640.jpg
http://www.swtpc.com/mholley/DC_5/ParallelCable640.JPG

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Michael Holley
www.swtpc.com/mholley
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