Post by thread:[PICS] Interrupt on change

Bob Blick <spam_OUTpicsTakeThisOuTparallaxinc.com> wrote: > It's my understanding that if interrupt-on-change is enabled, it is > enabled for all four pins(RB4,5,6,7), no choosing. Let's use a > PIC16C72 as an example. > > I'm not clear on the use of those four pins if some are used solely > as output pins. My questions are: > > If I use two of the pins(RB4,5) for outputs, the other two(RB6,7) > for inputs, and enable interrupt-on-change, will my manipulation of > the two output pins cause an interrupt, or otherwise mangle the > correct operation of the interrupt? Bob: No. The change-on-portb interrupt is only triggered when INPUT pins change states. > Second question: will reading port B mess with the use of the > interrupt-on-change feature? Probably. If a change occurs just as a read operation is being performed on port B, no interrupt will be generated. Worse, it seems that even WRITING to port B can make the PIC miss interrupts, since ALL register accesses (even MOVWF, etc.) perform a read first. > Do I need to use the first four pins(RB0,1,2,3) of port B > output-only if I enable interrupt-on-change? Must I read port B only > when servicing the interrupt? Doing those things will HELP the situation, but they won't guarantee that you'll never miss interrupts. In general, the only time the change-on-portb interrupts are truly reliable is when they're used to wake the processor from Sleep Mode. As I said in the answer to a similar question posted to my company's web page, "Sucks, don't it?" Sorry to be the bearer of bad news. -Andy === Andrew Warren - .....fastfwdKILLspam@spam@ix.netcom.com === === Fast Forward Engineering - Vista, California === === === === Custodian of the PICLIST Fund -- For more info, see: === === http://www.geocities.com/SiliconValley/2499/fund.html ===