Disable Encoders Problem

[TimCraig]

Originally Posted by Qbranch

Make sure to && your interrupt flag with the interrupt enable bit. When interrupt enable is off there will be no jump to the interrupt vector, but the flag will still get set.

I've never understood the && with the enable bit in the interrupt handler. If the interrupt isn't enabled, there will be no jump to the interrupt vector so that test will never be executed. Without the interrupt enabled, it's just an ordinary input pin.

[Kevin Watson]

Originally Posted by TimCraig

I've never understood the && with the enable bit in the interrupt handler. If the interrupt isn't enabled, there will be no jump to the interrupt vector so that test will never be executed. Without the interrupt enabled, it's just an ordinary input pin.

Yes, it's weird but Qbranch/Alex is correct. The interrupt flag gets raised (set to one) even if the interrupt is disabled.

-Kevin

[Alan Anderson]

Originally Posted by TimCraig

I've never understood the && with the enable bit in the interrupt handler. If the interrupt isn't enabled, there will be no jump to the interrupt vector so that test will never be executed. Without the interrupt enabled, it's just an ordinary input pin.

There is only one (low-priority) interrupt handler. It will be called when any interrupt occurs, and the handler has to check all the possible sources in order to service the interrupt properly. The program won't know not to deal with a flag for a disabled interrupt unless you also check the associated enable bit. You don't really want a serial port interrupt to end up running the service routine for a "disabled" encoder.

[mftaberner]

Thanks for all the help.

[TimCraig]

Originally Posted by Alan Anderson

There is only one (low-priority) interrupt handler. It will be called when any interrupt occurs, and the handler has to check all the possible sources in order to service the interrupt properly.

Yes, I understand this part. Not as nice as processors that have a separate vector for each interrupt but beggars can't be choosers, I guess.

Originally Posted by Alan Anderson

The program won't know not to deal with a flag for a disabled interrupt unless you also check the associated enable bit. You don't really want a serial port interrupt to end up running the service routine for a "disabled" encoder.

This is where I part company with MicroChip's implementation. If you don't enable the interrupt, it should never set the interrupt flag for that interrupt, in my opinion, because an interrupt should not have occurred. I guess one more reason I'll probably opt for something other than PICs for my personal projects.