Dave wrote:
>>> Does Mesa already
>>>       
> handle
> this protocol?
>
> Peter said that they can get the data into the hardware but that there 
> is no driver support for it yet.
>
> I need to get an SSI encoder.
>   
Well, it seems like it wouldn't be all that hard to adapt my PPMC 
encoder card to handle this
protocol, or maybe make an SSI to quadrature converter.  If the SSI code 
can be interrogated
fast enough, then the delay caused by converting serial to quadrature 
won't bother the loop
stability much.  I'm guessing from some of the data I read that the 
encoder could be read out
perhaps every 20 us or so.

The advantage of making an SSI to quadrature converter is that there 
won't be any driver
issues, and then the encoder can be used with a variety of servo 
systems.  I have this board
that I made for Fanuc encoders, but it has both differential receivers 
and drivers and a
Xilinx XC2C128 CPLD, which might have enough capacity to do the conversion.

If you have a small encoder I could borrow for a few weeks, I would like 
to give it a
try.


Jon

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