[Coco] Multicomp

[Dave Philipsen]

There have been a few who have expressed interest in the Multicomp FPGA 
computer designed by Grant Searle using John Kent's 6809 core. The 
project is found here: http://searle.hostei.com/grant/Multicomp/index.html

The schematic shows you how to connect a PS/2 keyboard to the Multicomp 
but some keyboards don't work.  This is because the original PS/2 
connector is designed for 5-volt operation and the FPGA project uses 3.3 
volts.  Most but not all PS/2 keyboards will tolerate 3.3 volt power.  
Some will work for awhile and then they will act flaky from time to 
time.  You can modify the circuit by adding four extra parts; two zener 
diodes and two resistors.  The FPGA dev board is powered by 5 volts so 
you can wire the keyboard according to the schematic found here: 
http://www.davebiz.com/coco/Searle-Multicomp-revision.pdf

Now the project should work well with any PS/2 keyboard and even some 
USB keyboards with a USB-PS/2 adapter.


Dave Philipsen