Re: Homebrew STG card - PAR-PORT

["Arne Chr. Jorgensen" <instel-at-online.no>]

On Tue, 07 Mar 2000, you wrote:

>The reason is to allow a step rate which has nothing to do with the
>cycle rate of the routine on the main CPU which generates the steps.
>The old program cycled at fixed time intervals, and could either
>generate a step pulse, or not.  This leads to very large jumps in step
>rate when you get near the maximum (ie. one step every cycle,
>one every 2 cycles, every 3 cycles, etc.)
>
>Jon

Sorry Jon,

I have been a bit confused -  when I think back ( not checking, so my memory
could be wrong )  8253 is a timer and 8254 is the improved version that will
work on a  8MHz bus.    Sure I do understand you would like a timer,  
the thing is that I mixed it with the 8255,  which should be a parallell driver
with handshake etc.  

This is what I was had in mind.  Sorry.   It is just that I have come across
this before,  people more or less insisting on a 8255,  something I don't see
the big benefit in.  This is what I meant with the 6821 ( I hope my memory is
correct :)  but this was a  PIA   adapter that could set any pin as either
input or output.  It is a motoralla circuit and there is problems to connect it
to a intel bus.  

A timer make sense,  sorry .


//ARNE