Interrupt on pin change

[phaedrus]

Hi ,

In the datasheet of 16F819,it is mentioned :

The interrupt-on-change feature is recommended for
wake-up on key depression operation and operations
where PORTB is only used for the interrupt-on-change
feature. Polling of PORTB is not recommended while
using the interrupt-on-change feature.

I am unable to understand the reason for this condition.
In my application,RB0 is used as an edge triggered interrupt,while RB1~RB3 are used as polled inputs.I wish to use RB4 as an "interrupt-on-change ".RB5~RB7 are used as outputs.
Would this be doable ?

 

[Pommie]

If you're continually polling portb then you may miss some interrupts.

Mike.

 

[phaedrus]

You mean it would not vector to the ISR,because the RBIF flag is cleared during the polling read ?

 

[Pommie]

I believe (but can't find where I read it) that if you read the port at the same time as a pin changes then the interrupt flag doesn't get set and therefore no interrupt is generated.

Mike.

 

[BeerBelly]

I wrote a program where the input would be polled in a loop. It would wait in this loop for an input.
It had me confused, Why was it not seeing any input and was stuck in this loop?
I realized that it never saw the input because it was interrupted every time it had an input.

 

[phaedrus]

Could not quite understand that.Did you have "interrupt on change" enabled ? Even then it should read the input,if you reset the RBIF flag in the ISR.

 

[BeerBelly]

I wish I could remember all the details. I'll have to see what I put in my notebook under stupid mistakes. It's heck being a senior.