PIC18F2480/2580/4480/4580
EXAMPLE 13-1:
IMPLEMENTING A REAL-TIME CLOCK USING A TIMER1 INTERRUPT SERVICE
RTCinit
MOVLW
MOVWF
CLRF
80h
TMR1H
TMR1L
; Preload TMR1 register pair
; for 1 second overflow
MOVLW
MOVWF
CLRF
b’00001111’
T1OSC
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
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
on Page:
INTCON
PIR1
GIE/GIEH PEIE/GIEL TMR0IE
INT0IE
TXIF
RBIE
SSPIF
SSPIE
SSPIP
TMR0IF
CCP1IF
CCP1IE
CCP1IP
INT0IF
TMR2IF
TMR2IE
TMR2IP
RBIF
55
58
58
58
56
56
56
PSPIF(1)
PSPIE(1)
PSPIP(1)
ADIF
ADIE
ADIP
RCIF
RCIE
RCIP
TMR1IF
TMR1IE
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.
Note 1: These bits are unimplemented on PIC18F2X80 devices; always maintain these bits clear.
© 2009 Microchip Technology Inc.
DS39637D-page 159
MICROCHIP [ MICROCHIP ]
