Post by thread:PIC 16c71

> I'm am having problems with the rtcc interupt on the '71. Could you describe the problem in more detail? General hints: 1. Make sure you turn on the GIE bit and the T0IE bit in the INTCON register when your code is prepared to deal with interrupts. 2. Clear the T0IF bit before turning on the enable bits (as in hint 1), or you may get an immediate unexpected interrupt because the timer may have already overflowed previously. 3. Make sure your interrupt handler saves and restores W and STATUS properly. It is tricky to restore without changing STATUS; the SWAPF instruction must be used. The 16C7x data sheet has suggested code in section 14.6. Also, you may need to save other registers such as FSR or PCLATH if your interrupt handler changes them. 4. The interrupt handler must clear the T0IF bit in the INTCON register before it returns in order to clear the interrupt condition. Otherwise the interrupt handler will get called continuously. 5. The interrupt handler must use the RETFIE instruction to return, or the GIE bit will stay clear and you won't get any more interrupts after the first one. 6. If your code ever needs to turn off the GIE bit (global interrupt enable), make sure you read Microchip application note 576. There can be a problem if an interrupt happens during the execution of the instruction that turns off GIE. It is generally easier to turn off only the specific interrupt enable bit(s) that you care about, such at T0IE. 7. Make sure interrupts are disabled before you execute any instruction that directly writes to the PCL register, such as an ADDWF PCL (typically used in a table look-up). According to application note 556, an interrupt that happens during the instruction that changes the PCL can return to the wrong place (the desired address + 1). I asked about this problem in the recent seminar and the Microchip people who were present think that this application note may be incorrect and that the part may handle this situation properly. Cheers, Eric http://www.telebit.com/~eric/pic/