Real-time clock

[DriverInside]

Hello i'll like to use the TIMER1 as a real time clock with my pic18F4455... I founded this code in the 18F datasheet.

I'll like to know how the use assembler code in a C program and how can a read/change the present time.

thank you

JP

//==============================================
// Real time clock
//==============================================

RTCinit
MOVLW 80h ; Preload TMR1 register pair
MOVWF TMR1H ; for 1 second overflow
CLRF TMR1L
MOVLW b’00001111’ ; Configure for external clock,
MOVWF T1OSC ; Asynchronous operation, external oscillator
CLRF secs ; Initialize timekeeping registers
CLRF mins ;
MOVLW d’12’
MOVWF hours
BSF PIE1, TMR1IE ; Enable Timer1 interrupt
RETURN
RTCisr
BSF TMR1H, 7 ; Preload for 1 sec overflow
BCF PIR1, TMR1IF ; Clear interrupt flag
INCF secs, F ; Increment seconds
MOVLW d’59’ ; 60 seconds elapsed?
CPFSGT secs
RETURN ; No, done

CLRF secs ; Clear seconds
INCF mins, ; Increment minutes
MOVLW d’59’ ; 60 minutes elapsed?
CPFSGT mins
RETURN ; No, done

CLRF mins ; clear minutes
INCF hours, F ; Increment hours
MOVLW d’23’ ; 24 hours elapsed?
CPFSGT hours
RETURN ; No, done

MOVLW d’01’ ; Reset hours to 1
MOVWF hours
RETURN ; Done

[ckielstra]

You can use assembler in your program using the #ASM and #ENDASM directives, check the manual for examples.

Much easier is to use the search function of this forum (see top of the page) and use one of the C implementations, for example http://www.ccsinfo.com/forum/viewtopic.php?p=59789#59789