PIC18F2450 Datasheet, PDF (121/320 Pages) Microchip Technology – 28/40/44-Pin, High-Performance, 12 MIPS, Enhanced Flash, USB Microcontrollers with nanoWatt Technology

PIC18F2450/4450
EXAMPLE 11-1: IMPLEMENTING A REAL-TIME CLOCK USING A TIMER1 INTERRUPT SERVICE
RTCinit
RTCisr
MOVLW
MOVWF
CLRF
MOVLW
MOVWF
CLRF
CLRF
MOVLW
MOVWF
BSF
RETURN
80h
TMR1H
TMR1L
b’00001111’
T1OSC
secs
mins
d’12’
hours
PIE1, TMR1IE
; Preload TMR1 register pair
; for 1 second overflow
; Configure for external clock,
; Asynchronous operation, external oscillator
; Initialize timekeeping registers
;
; Enable Timer1 interrupt
BSF
BCF
INCF
MOVLW
CPFSGT
RETURN
CLRF
INCF
MOVLW
CPFSGT
RETURN
CLRF
INCF
MOVLW
CPFSGT
RETURN
MOVLW
MOVWF
RETURN
TMR1H, 7
PIR1, TMR1IF
secs, F
d’59’
secs
secs
mins, F
d’59’
mins
mins
hours, F
d’23’
hours
d’01’
hours
; Preload for 1 sec overflow
; Clear interrupt flag
; Increment seconds
; 60 seconds elapsed?
; No, done
; Clear seconds
; Increment minutes
; 60 minutes elapsed?
; No, done
; clear minutes
; Increment hours
; 24 hours elapsed?
; No, done
; Reset hours to 1
; Done
TABLE 11-2: REGISTERS ASSOCIATED WITH TIMER1 AS A TIMER/COUNTER
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset
Values
on page
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE
RBIE TMR0IF INT0IF
RBIF
49
PIR1
—
ADIF
RCIF
TXIF
—
CCP1IF TMR2IF TMR1IF
51
PIE1
—
ADIE
RCIE
TXIE
—
CCP1IE TMR2IE TMR1IE
51
IPR1
—
ADIP
RCIP
TXIP
—
CCP1IP TMR2IP TMR1IP
51
TMR1L Timer1 Register Low Byte
50
TMR1H TImer1 Register High Byte
50
T1CON
RD16 T1RUN T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON 50
Legend: — = unimplemented, read as ‘0’. Shaded cells are not used by the Timer1 module.
© 2006 Microchip Technology Inc.
Advance Information
DS39760A-page 119