I suppose if you have already moved to the 628 its probably not practical,
but I imagine you could quite likely use the 877 PWM with a low frequency
setting to generate a nice consistant pulsestream and then update the
frequency each time you receive a new serial packet. You might need to keep
track of how many output pulses the PWM has actually made to synchronise
with your serial input data but then the serial stream would be less time
critical.

James


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Alan B. Pearce
Sent: Monday, June 24, 2002 9:36 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Serial timing dilemma


Not clear to me just what the motors are driving. Is it an indicator or does
it feed back to the gyro by changing the vehicles direction?

In order to fix your problem I suspect you may have to do something to get
your motors to move within the shortest update period. From your description
I take it they are stepper motors. Then you may have to ramp up the stepping
rate to a speed that allows them to complete the movement inside the time
period, and ramp down again.

Do you really need the dead time while receiving the data stream? I would
have thought a suitable interrupt driven set of routines would have handled
two motors and a serial stream with ease.

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