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| Micro Controllers Discuss all aspects of micro controllers - building them, coding them, etc. All controllers are welcome - PIC, BASIC, Z8 Encore!, etc. |
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21st May 2004, 10:45 PM
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 Interrupt on GP Change problem I've been working with this for a couple days, and can't get it to behave properly. This minimal code should use interrupts to simply set the output state based on the input state. I've tried this without interrupts (basically just using the interrupt handler as the main loop) and it works fine, so I know my inputs and outputs are right. Any insight as to why this doesn't work will be greatly appreciated! Code: #define BUTTON_BIT 2 #define OUTPUT_BIT 4 LIST p=12F629 include "P12F629.inc" __config b'10000110000100' org 0x0000 goto Setup org 0x0004 goto Interrupt Setup ;turn comparators off movlw 0x07 movwf CMCON bsf STATUS, RP0 ;Bank 1 ;Specify input ports clrf TRISIO bsf TRISIO, BUTTON_BIT ;Enable pull up on input clrf WPU bsf WPU, BUTTON_BIT ;Set interrupt on change for input clrf IOC bsf IOC, BUTTON_BIT ;Callibrate internal oscillator call 3FFh movwf OSCCAL ;Set options (enable global weak pull ups) movlw b'01111111' movwf OPTION_REG bcf STATUS, RP0 ;Bank 0 ;Read input state movf GPIO,w ;Enable global interrupts and GPIO change interrupt bsf INTCON, GPIE bsf INTCON, GIE ;infinite loop goto $ Interrupt ;Clear interrupt flag bcf INTCON,GPIF ;Set output based on input state btfss GPIO,BUTTON_BIT goto $+3 bsf GPIO,OUTPUT_BIT goto $+2 bcf GPIO,OUTPUT_BIT retfie end | |
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22nd May 2004, 02:39 PM
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| I did some more testing and I think I have a better handle on the problem. It seems that an interrupt is only being generated when the input goes high, but not when it goes low. I thought an interrupt would be generated in both cases. Am I misinterpreting the datasheet? Dan East | |
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22nd May 2004, 06:12 PM
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| Okay, I've gotten it to work after modifying my circuit, however I'm not exactly sure why it wouldn't work properly before. I'm using the internal pull up, and pulling the pin low externally using a 560 ohm resistor. Now as I said, if I read the pin state in a loop without using interrupts it behaves as it should - the GPIO state matches the physical switch. So I tried removing the 560 ohm resistor, and that correct the problem - the interrupts now work properly. So I can only surmise that the input tolerances required to trigger an interrupt are somehow different than those required to set the pin state. My guess is there is some logic used to properly interpret analog input so it will correctly trigger interrupts on a digital input, and since I wasn't pulling it all the way down to 0 volts it wasn't resetting that logic. Maybe this will save someone else some trouble in the future.  Dan East | |
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Linear Mode
