PIC18F2331/2431/4331/4431
EXAMPLE 13-1:
IMPLEMENTING A REAL-TIME CLOCK USING A TIMER1 INTERRUPT SERVICE
RTCinit
MOVLW
MOVWF
CLRF
0x80
TMR1H
TMR1L
; Preload TMR1 register pair
; for 1 second overflow
MOVLW
MOVWF
CLRF
b'00001111'
T1CON
secs
; Configure for external clock,
; Asynchronous operation, external oscillator
; Initialize timekeeping registers
;
CLRF
mins
MOVLW
MOVWF
BSF
.12
hours
PIE1, TMR1IE
; Enable Timer1 interrupt
RETURN
RTCisr
BSF
BCF
INCF
MOVLW
TMR1H, 7
PIR1, TMR1IF
secs, F
.59
; Preload for 1 sec overflow
; Clear interrupt flag
; Increment seconds
; 60 seconds elapsed?
CPFSGT secs
RETURN
; No, done
CLRF
INCF
MOVLW
secs
mins, F
.59
; Clear seconds
; Increment minutes
; 60 minutes elapsed?
CPFSGT mins
RETURN
; No, done
CLRF
INCF
MOVLW
mins
hours, F
.23
; clear minutes
; Increment hours
; 24 hours elapsed?
CPFSGT hours
RETURN
; No, done
MOVLW
MOVWF
RETURN
.01
hours
; Reset hours to 1
; Done
TABLE 13-2: REGISTERS ASSOCIATED WITH TIMER1 AS A TIMER/COUNTER
Reset Values
on Page:
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
INTCON GIE/GIEH PEIE/GIEL TMR0IE
INT0IE
TXIF
RBIE
SSPIF
SSPIE
SSPIP
TMR0IF INT0IF
RBIF
54
57
57
57
55
55
55
PIR1
—
—
—
ADIF
ADIE
ADIP
RCIF
RCIE
RCIP
CCP1IF TMR2IF TMR1IF
CCP1IE TMR2IE TMR1IE
CCP1IP TMR2IP TMR1IP
PIE1
TXIE
TXIP
IPR1
TMR1L
TMR1H
T1CON
Timer1 Register Low Byte
Timer1 Register High Byte
RD16 T1RUN T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the Timer1 module.
2010 Microchip Technology Inc.
DS39616D-page 135
MICROCHIP [ MICROCHIP ]
