Post by thread:Simple RB0/INT setup question.

Hello piclisters! I want to use an external interrupt source (on RB0/'INT) to wake up my PIC from SLEEP . Are these previous steps OK? LIST p=16F84 include <p16f84.inc> ; compiled with MPASM v02.13 ORG 0 goto start nop ;filling the gap with nops up to 0x4 nop nop ORG 4 goto inter ;INT/RB0 should put PC here (0x0004) when droppe d LOW start bcf INTCON,GIE ;disable global int. bit btfsc INTCON,GIE ;test if done goto start ;not done, retry bsf INTCON,INTE ;use RB0 as external interrupt source bsf STATUS,RP0 ;select mem bank 1 bcf 0x1,INTEDG ;interrupt on falling edge (0x1 is option reg.) movlw b'00000110' ;hate this bank switching stuff! movwf 0x5 ;0x5 is trisa ;RA0 output, RA1 & RA2 inputs bsf 0x6,0 ;set RB0 as input (0x6 is trisb) ;(Must I set RB0 as an input in order to get it ; to work as an external interrupt?) bcf STATUS,RP0 ;back to bank 0 clrf FSR ;clear indirect addr. reg. bsf PORTA,0 ;RA0 HIGH bsf INTCON,GIE ;enable global interrupts sleep ;0004h : We should get here when interrupted inter bcf INTCON,GIE ;disable ints while in this routine [some more code] goto loop [some more code] ;must I enable global int bit before 'sleeping'? sleep ;Can I do this? loop [some more code] sleep ;Will sleep always be coming back to 0x4 vector? Is it OK not to use RETFIE ? Will this pseudo code put the program counter at 0x4 every time RB0 pin switches from HIGH to LOW? Sorry, I'm confused! P.D: Thanks to James Cameron and Regulus Berdin for their help on coding. -------------------------------------------- "I must not fear. Fear is the mind-killer. Fear is the little death that brings total obliteration. I will face my fear... I will permit it to pass over me and through me." Kwisatz Haderach - Dune netQ <spam_OUTnetquakeTakeThisOuTinnocent.com>

netQ wrote: > > Hello piclisters! > > start bcf INTCON,GIE ;disable global int. bit > btfsc INTCON,GIE ;test if done > goto start ;not done, retry Probably not necessary to do this because the GIE bit = 0 on power up. > bsf 0x6,0 ;set RB0 as input (0x6 is trisb) > ;(Must I set RB0 as an input in order to get i t ; to work as an > external interrupt?) For normal RB0Int use, yes. I think you can also trigger this interrupt, if enabled, if RB0 is set as an output because the input circuits are also connected to the output drivers. > bcf STATUS,RP0 ;back to bank 0 > clrf FSR ;clear indirect addr. reg. > bsf PORTA,0 ;RA0 HIGH > bsf INTCON,GIE ;enable global interrupts > sleep You should have a loop here because the PC will end up pointing to an instruction following SLEEP, which you don't have. Try this.. Loop sleep nop goto Loop The 'nop' is executed after the interrupt occurs and before the interrupt routine begins. > inter bcf INTCON,GIE ;disable ints while in this routine > [some more code] > goto loop > [some more code] ;must I enable global int bit before 'sleeping '? > sleep ;Can I do this? > > loop [some more code] > sleep ;Will sleep always be coming back to 0x4 vecto r? The GIE bit is automatically cleared when an interrupt is responded to so you do not need 'bcf INTCON,GIE'. Instead you need to clear the RB0Int flag, otherwise the interrupt will recur when the GIE bit is set to 1 again. You should have a RETFIE to finish your interrupt routine. Then after that executes, the 'goto sleep' instruction will execute and put the PIC back to sleep. inter bcf INTCON,INTE ;clear int. bit [some more code] goto loop [some more code] retfie loop [some more code] retfie > Is it OK not to use RETFIE ? I gather that you want to keep waking the PIC each time an RB0Int occurs, so you need to use the RETFIE instruction to reenable the RB0INT interrupt. If you omit the RETFIE and use a RETURN, then the interrupt will not happen again because GIE will stay = 0. If you do not use either of these instructions then the stack will overflow. > Will this pseudo code put the program counter at 0x4 every time RB0 pin > switches from HIGH to LOW? If the PIC is asleep AND the GIE bit = 1, then after the RB0Int interrupt occurs, the instruction following the sleep instruction is executed and then the PC is loaded with address 0004h. Hope this helps. -- Best regards Tony Multimedia 16F84 Beginners PIC Tools. **New Improved PicNPost** http://www.picnpoke.com Email .....picnpokeKILLspam@spam@cdi.com.au