I've just produced my first prototype PIC circuit, and last night got it
working exactly as required.

The main problems I had to fix were TMR0 related, as I didn't simulate these
functions to test them as it took too long.

There is one that I would like to see if there is a better solution for:

The setup is:

PIC16F84 with 4MHz clock
TMR0 driven from the external clock
the prescaler assigned to TMR0 and set to /256
load TMR0 with 0x3D, so that TMR0 increments 195 time before wrapping

This generates an interrupt from the timer wrap every 50ms or so. I want
this timer to keep running, so as part of the interrupt handler, I reprime
TMR0 with 0x3D to wait for another 50ms, but in doing so, I discovered, this
turns off the prescaler. So my fix was also to reset the OPTION byte to
reassign the prescaler each time I reprime TMR0.

This works fine, but I am worrying slightly that:

a) it seems a little clunky
b) there is a gap between repriming TMR0 and reassigning the prescaler where
TMR0 is running at full speed

So what have you all done out there?

Thanks,

Andy



--
Andy Baker  mailto:ab@datcon.co.uk
ATM, MPLS and Telecoms Development Group
Data Connection Ltd., Chester, UK
http://www.datcon.co.uk/
Tel: +44 (0) 1244 313440  Fax: +44 (0) 1244 312422