On Wed, 28 Jul 2010, Drew Maurer wrote:

> Another, related, question - what happens to the USART when the TMR0
> interrupt fires?  Does it finish sending the byte normally?  Reason being=
,
> this is a servo driver/current monitor for my lonelybot.com project - the
> TMR0 interrupt is used to generate the 20ms "off" time for the servo's PW=
M
> input; when the 20ms is up, the interrupt holds control for the 1-2ms ser=
vo
> pulse.  4800 baud means that my data strings collide with the interrupt
> frequently - my testing shows that, at 4800 baud almost 70% of my strings
> collide with the interrupt in this way, which is unacceptable because I h=
ave
> to repeat the request 5 or 10 times which is really going to flood the da=
ta
> bus on my boat.  Can I ignore these interrupts in my data?  Am I guarante=
ed
> that the data is still good, just delayed?

Doing the servo pulse timing as you describe is reasonable if you are=20
controlling multiple servos. Consider using two PICs, one for the servo=20
control and one for the comms. You could get the comms PIC to buffer data=20
and present it to the servo controller as fast (high speed bursts "packet=20
at a time" over SPI) or slow (byte at a time as requested) as you want.

Regards
Sergio Masci
--=20
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