Sorry Kirk, I wasn't referring to recent post....I should have specified
that. A while back the discussion started out with digital I/O but if I
remember correctly it went to issues of timing and servos. I believe it
was dropped because it was thought to be unsafe. The only point I was
trying to make was that the option to use it or not should remain with
the end user and integrator, and that careful planning is required by
the integrating person(s) to ensure the safe operation of the machine
for the sake of the operator and machine. I think that safety is being
being addressed by all involved in this project and great lengths are
being taken to provide that safety. My goal is not to offend, only to
help in any way possible to help progress with EMC. Again, offense is
not my goal and you have my apology! I do agree with your view on
spindle operation timing. I just wouldn't trust it with servos. Just my
view.
Thanks for your comment,
Dave
On Thu, 2008-10-23 at 08:33 -0700, Kirk Wallace wrote:
> On Thu, 2008-10-23 at 10:36 -0400, Dave Keeton wrote:
> > I think that using Modbus to operate a vfd for spindle control is ok,
> > but again the discussion is going back to issues of timing critical
> > functions such as motor and drive control.
> ... snip
> > Dave
>
> I agree that Modbus should only be used for non-reatime functions, but I
> didn't see anyone suggest to the contrary in the recent posts. I did try
> to imply that whatever HAL component is written needs to do what it
> needs to do within the time available in the thread that it lives in. I
> had trouble with my SPI component due to this. I think just about
> everything you would want to with spindle speed and most other I/O can
> be done in non-realtime.
>
> This reminds me that there is a time critical element in ModBus in that
> the spec calls out timing constraints on the ACK or RTS or some such
> thing. It seemed that experts disagree to how handle the timing issues.
>
> Kirk
>
>
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