Interrupt based timer outputting wrong frequency
This object of the test program below is to toggle a LED at a 5 hz frequency. When the actual 12F1822 test circuit is run, the LED toggles at a 50 hz rate, confirmed by oscilloscope.
What seems to be happening is that the increment-to-count 10 part of the handler is not executing. The toggle frequency is determined only by the pre-scale and post- scale settings. Any ideas?
Code:*************************************** *Program to test timer 2 interrupt *Target processor is PIC 12f1822 *88 program words, revised 09/26/2011 *************************************** 'set 12f1822 configurat1on #CONFIG __config _CONFIG1, _FOSC_INTOSC & _MCLRE_OFF & _CLKOUTEN_OFF __config _CONFIG2, _PLLEN_OFF & _LVP_OFF #ENDCONFIG 'set registers OSCCON = 01101000 '4 mhz osc OSCTUNE = 0 'factory calibration ANSELA = 0 'all digital OPTION_REG.7 = 0 'global pullups enabled WPUA = 000100 'porta pin2 weak pullup enabled CM1CON0.7 = 0 'comparator disabled TRISA = 001111 'porta.5 and porta.4 are outputs, all others input INTCON = 11000000 'global and peripheral interrupts enabled PIE1 = 00000010 'enable tmr2 interrupt T2CON = 00011110 'turn on tmr 2 (bit 2),1:16 prescale,1:4 postscale PIR1.1 = 0 'clear tmr2 interrupt flag PR2 = 156 'preset for 100 hz interrupt define INTHAND clock goto overint asm clock INCF _ticks,f ;ticks=ticks + 1 MOVF _ticks,w ;read ticks into w SUBLW d'10' ;subtract w from decimal 10 BTFSS STATUS,2 ;zero? RETFIE ;return for next interrupt if not zero CLRF _ticks ;clear ticks count MOVLW b'00010000 ;load binary literal into w XORWF PORTA,f ;toggle porta pin4 BSF _tenths ;set tenths-changed flag BCF PIR1,1 ;reset tmr2 interrupt flag RETFIE ;return to main endasm overint: 'declare variables ticks var byte bank0 tenths var bit bank0 'initialize register functions porta.4 = 1 'initialize led off tenths = 0 'clear tenths-changed bit main: tenths = 0 'clear tenths-changed bit pause 1000 'wait 1 second goto main 'loop back to main
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