Keyboard PS/2 to Parallel converter

Jim Brain brain at
Wed Jan 9 01:59:19 CST 2008

Enrico Lazzerini wrote:
> Jim, 
> i need just this, I don't care to see the caps lock led turning on or off!!
> But the schematic indicated to that link, it appear to be a theoric
> schematic.
> I really have not time to testing circuit or verify how it works.
> So anybody has an idea of a pratical circuit working? 
Yes, the schematic won't work as-is (it's only 10 bits, and PS/2 uses 11 
(start, parity, stop, 8 bits) and as Holger notes, it just delivers PS/2 
Set 2 scan codes, which are horrid (voice of recent experience)

But, the design I already sent you will do exactly what you wish.  One 
Atmel Mega8 (or a Tiny24 would work, though I don't have any here to 
test the code).  Is there something else you're looking for?  I modified 
the PS2Encoder design on the web site 
( to offer a truly 
generic one (all data lines come to a 2x13 header, and the PS/2 
connector is already on the board.)

I know the design works, as I tested the code before I sent someone on 
the list a version for a FlashWriter II KB interface.

> Holger, 
> it's exactly what i'm looking for. So may you give your help? What PIC to
> use?
> I have a PS2 Keyboard and when I press the character A I need to have the 
> binary code 41H that means 0100 0001B on eight wires plus a strobe line. 
> Only in this direction. Is it possible?
> Thanks
> Enrico
Dave's code will work (though you'll need to write some additional 8051 
code to do the parallel output, should be trivial.

My code will work, and outputs 41H when a A is sent (Actually, I think 
it sends lowercase a, but I can change the mappings in a few minutes if 
that's an issue)

Holger is speaking theoretically, without any specific design in mind, I 


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