I am working on dual channel timer project. The timer will be used for my aquarium to turn-off and turn-on lights in needed intervals of time. The PCB is made, and almost all electronic parts is soldered. Now i am working with microcontroller coding, i am programming clock, which must count minutes and hours. Seconds is counted by Timer1, which works fine. In timer schematics i am using multiplexing (see schematics), multiplexing i am planning to make via timer0. But i can’t make to work timer0 like i want, seems like prescaler is not working. I programmed timer0 to do interrupts on overflow every 0,125sec (8Hz). On interrupt four led indicators HG1-HG4 must be switched and led HL5 must blink in rate of 8Hz. But insted of this HL5 is lit continously. i guess that interrupts occur so frequently, that the only one instruction of main program is executed, and then interrupt from timer0 occurs. Maybe someone could help me with this problem? CODE:

//Quartz crystal=2.097152Mhz, ucontroller – PIC16F873
/*Configuration:
oscilator XT; code protection off; WDT disabled; power-up timer enabled;
brown-out reset enabled; low voltage programming disabled;
code protection data disabled; flash program memory write enabled;
debugger mode disabled.
*/
//variable declaration
unsigned int Clock, Display;
unsigned short int a, Seconds,
T1on, T1off, T2on, T2off, Segment1, Segment2, Segment3, Segment4;

void zero(){PORTC=0b00111111;} //show number 0 in display
void one(){PORTC=0b00000110;} //show number 1 in display
void two(){PORTC=0b01011011;} //show number 2 in display
void three (){PORTC=0b01001111;} //show number 3 in display
void four (){PORTC=0b01100110;} //show number 4 in display
void five (){PORTC=0b01101101;} //show number 5 in display
void six (){PORTC=0b01111101;} //show number 8 in display
void seven (){PORTC=0b00000111;} //show number 7 in display
void eight (){PORTC=0b01111111;} //show number 8 in display
void nine (){PORTC=0b01101111;} //show number 9 in display

void interrupt () {

//interrupt from Timer1 – 1 sec (Seconds counter)
if(PIR1.TMR1IF==1){
if (Secondslt=58) {Seconds=Seconds+1;PORTA.B3=~PORTA.B3;}
else if (Seconds=59ampampClocklt=1438) {Seconds=0; Clock=Clock+1;}
else if (Seconds=59ampampClock==1439) {Seconds=0; Clock=0;};
PIR1.TMR1IF=0;} //clear TMR1 flag

//interrupt from Timer0 – 0.124 sec (Display multiplexing)
if(TMR0.T0IF==1){PORTA.B5=~PORTA.B5;
if (PORTB.B2==1) {PORTB.B2=0; switch (Segment2){
case 0: zero(); break;
case 1: one (); break;
case 2: two(); break;
case 3: three (); break;
case 4: four(); break;
case 5: five (); break;
case 6: six(); break;
case 7: seven (); break;
case 8: eight(); break;
case 9: nine (); break;};
PORTB.B1=1; PORTB.B0=0; PORTA.B0=0;
}

else if (PORTA.B0==1) {PORTA.B0=0; switch (Segment1){
case 0: zero(); break;
case 1: one (); break;
case 2: two(); break;
case 3: three (); break;
case 4: four(); break;
case 5: five (); break;
case 6: six(); break;
case 7: seven (); break;
case 8: eight(); break;
case 9: nine (); break;};
PORTB.B2=1; PORTB.B1=0; PORTB.B0=0;
}

else if (PORTB.B0==1) {PORTB.B0=0; switch (Segment4){
case 0: zero(); break;
case 1: one (); break;
case 2: two(); break;
case 3: three (); break;
case 4: four(); break;
case 5: five (); break;
case 6: six(); break;
case 7: seven (); break;
case 8: eight(); break;
case 9: nine (); break;};
PORTA.B0=1; PORTB.B1=0; PORTB.B2=0;
}

else if (PORTB.B1==1) {PORTB.B1=0; switch (Segment3){
case 0: zero(); break;
case 1: one (); break;
case 2: two(); break;
case 3: three (); break;
case 4: four(); break;
case 5: five (); break;
case 6: six(); break;
case 7: seven (); break;
case 8: eight(); break;
case 9: nine (); break;};
PORTB.B0=1; PORTA.B0=0; PORTB.B2=0;
}
TMR0.T0IF=0;};//clear TMR0 flag
}

void main() {
/*SFR’s and variables initialisation*/
ADCON1=0b00000110; //make PORTA pins digital
TRISA=0b00000000; //configure input/output pins, turn on Clock indication
TRISB=0b11110000;
TRISC=0b00000000;
PORTA=0b00111000; //clear data latches
PORTB=0b00000100;
PORTC=0b00000000;
OPTION_REG.B7=0; //turn on pullups for B port
Seconds=0; Clock=0; //Set all variables to zero
T1on=0; T1off=0; T2on=0, T2off=0;
Segment1=0;
Segment2=0;
Segment3=0;
Segment4=0;
Display=0;
a=0;

// Timer0 initialisation (Display multiplexing) Period = 0.125 sec (8Hz)
OPTION_REG.T0CS = 0; // TMR0 Clock Source Select bit – Internal Clock
OPTION_REG.PSA = 0; // prescaler is assigned to the Timer0
OPTION_REG.PS2 = 1; // Prescaler= 256
OPTION_REG.PS1 = 1;
OPTION_REG.PS0 = 1;
TMR0 = 1; // preset for timer register
TMR0.T0IF=0; //clear TMR0 interrupt flag
INTCON.T0IE=1; //TMR0 interrupt enable

// Timer1 initialisation (Seconds counter) Period = 1 sec
T1CON.T1CKPS1 = 1; // Prescaler= 8
T1CON.T1CKPS0 = 1;
T1CON.T1OSCEN = 0; // Timer1 Oscillator disable
T1CON.TMR1CS = 0; // Timer1 Clock Source Select bit – internal clock
T1CON.TMR1ON = 1; // enable timer
TMR1H = 0; // preset for timer1 MSB register
TMR1L = 0; // preset for timer1 LSB register
PIR1.TMR1IF = 0; //clear TMR1 interrupt flag
PIE1.TMR1IE=1; //TMR1 interrupt enable

/*
//Timer2 initialisation (Display multiplexing) Period = 0.1245 sec
T2CON = 120; // Postscaler=16
T2CON.TMR2ON = 1; // turn timer2 on;
T2CON.T2CKPS1 = 1; // Prescaler=16
T2CON.T2CKPS0 = 0;
PR2 = 255; // PR2 (Timer2 Match value)
PIR1.TMR2IF = 0; // clear timer2 interupt flag
PIE1.TMR2IE = 1; // enable Timer2 interrupts
*/
INTCON.PEIE = 1; //Peripheral Interrupt Enable
INTCON.GIE = 1; // global interrupt enable

for (;;) {
Display=Clock; //on turn-on show Clock time in display
Segment1=Display/600; //calculate hours
Segment2=Display/60;
a=Display%60; //calculate minutes
Segment3=a/10;
Segment4=a%10;
}
}

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