Sync ADC Reading with PWM

[dmccric]

Hello,

I am using the PIC18F4431 and need to know how to sync the reading of the adc when the PWM pin is high. At the moment I am using the standard adc reading but this is inaccurate.

Cheers

Dave

[PCM programmer]

You could poll the INT_TIMER2 interrupt flag in a loop. When it goes
high it means a PWM cycle has started. You could read the ADC at that
time. See this example code which tests the INT_TIMER2 flag:
http://www.ccsinfo.com/forum/viewtopic.php?t=41403&start=5

Or if you want to do it inside an interrupt routine, this code shows how
to use the Timer2 interrupt. The PWM cycle starts when the
#int_timer2 interrupt occurs. But, if your PIC is running at a low
frequency, such as 4 MHz, there can be a 25 to 30 usec delay between
the time the Timer2 interrupt occurs, and time that it enters into the
#int_timer2 interrupt routine. This is the time required by the CCS
interrupt handler to "save the state of the machine" and to route to
the #int_timer2 routine.
http://www.ccsinfo.com/forum/viewtopic.php?t=41473&start=1

[bkamen]

If you look closely at the ADCON3 register, you'll see you can trigger the A/D to take a measurement on several source inputs as the trigger. One of them being the PowerPWM.

Then you could have an IRQ for the A/D to just get the data when ready.

I did this in the past and it works nice.

You don't even need to set IRQ's for the PPWM unit.. just enable it and set the trigger for the A/D as needed.

Then it's all done in hardware with the only IRQ being the A/D when the result is ready.

-Ben
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