Re: EMC compatible computers

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

John Sheahan wrote:

>On Mon, Jan 13, 2003 at 06:41:02PM -0500, alex wrote:
>  
>
>>There is a possibility of another hardware model without a  high cost.
>>Consider a controller which consists of several low-speed mother boards
>>connected together
>>either through the parallel data link or the ethernet. 
>>    
>>
>
>remember the parallel port is dying. ethernet will be around longer.
>the cost of interfacing to either is tiny compared to 
>other related costs.
>
>And the parallel port (electrical) performance sucks compared to any 
>ethernet - particularly optical ones. 
>  
>
Well, I have run a 3-axis servo update cycle, all using floating-point 
calculations for a
PID plus feed-forward routine, on a 333 MHz Pentium-II in 50 uS, 
controlling my PPMC
hardware through the parallel port.  Minimal protocol overhead on this. 
 That time is
measured from the first command, which latches all the encoder counts, 
to the last
command, which causes the velocity DACs to update.

Jon