Re: [Emc-users] Re: pci motion control card

[Jon E. <el...@pi...>]

Abdul R Rafiq wrote:

>I have a question on the watchdog circuit.
>
>In my design, the watchdog circuit can be configured to timeout in 125, 250,
>500 and 1000 milli sec.  Is this something that is useful or just one
>timeout value is fine?  If multiple settings are not needed, then what is a
>good timeout value that emc can keep up with?
>  
>
What is your servo update rate?  I use 1 mS (1000 Hz) but could go faster
if there was any reason to.  Something in the 5-20 mS range seemed good,
as the machine couldn't get too far in that short interval.  125 mS is 
very large,
1000 mS is totally useless, even a human could often respond that fast!

>the watchdog circuit gets reset by writing to the DACs, outputs, step
>generators, or the manual reset address.  when the wd timesout, it holds the
>dac, step gen and outputs in off state until a software or hardware reset.
>by default the watchdog circuit is disabled.
>  
>
I just made sure that the first two DACs got written, and called that 
good enough.
That seemed the most critical function, that the servos were still under
CPU control.  I have a jumper on the circuit board to enable/disable the
watchdog.  The watchdog is reset any time the DACs are written to, and then
the CNC program can bring the machine out of estop.

Jon