Re: digital servo controller to offload the Parallel Port?

[Jon Elson <elson-at-pico-systems.com>]

John Griessen wrote:

>Les,
>
>I understand that emc uses the low cost of the mass produced PC to great
>effect.   It just seemed Till knew where a performance limit was when
>using the parallel port, and I was asking.  I have not played with an
>emc driven machine yet.  Is there anyone in  Austin TX using one?
>  
>
There is not any real practical limit that you need to be concerned 
about.  The one place there
seems to be one is in the area of SOFTWARE generated step pulses.  This 
is a result of trying
to do pulse timing essentially with either polled timing or timing 
loops, on a multi-tasking
system.  UGH!  A HORRIBLE idea!

I have the step pulse generation in an FPGA, controlled by the parallel 
port.  I can send data
bytes at the rate of one every 800 nS or so (that's 1.2 million/second) 
through the parallel
port.  My servo control routines update the whole servo system for 3 
axes in 50 uS on a
333 MHz Pentium-II, so you could easily go to a 10 KHz servo update rate 
and still leave
50% of the CPU available!

So, the parallel port, itself, is not the limit, but software timing is.

Jon