Microchip Technology DM183021 Data Sheet

 2010 Microchip Technology Inc.

DS39616D-page 135

PIC18F2331/2431/4331/4431

EXAMPLE 13-1:

IMPLEMENTING A REAL-TIME CLOCK USING A TIMER1 INTERRUPT SERVICE

TABLE 13-2:

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

PIR1

—

ADIF

RCIF

TXIF

SSPIF

CCP1IF TMR2IF TMR1IF

PIE1

—

ADIE

RCIE

TXIE

SSPIE

CCP1IE TMR2IE TMR1IE

IPR1

—

ADIP

RCIP

TXIP

SSPIP

CCP1IP TMR2IP TMR1IP

TMR1L

Timer1 Register Low Byte

TMR1H

Timer1 Register High Byte

T1CON

RD16

T1RUN

T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON

Legend:

— = unimplemented, read as ‘0’. Shaded cells are not used by the Timer1 module.

RTCinit

MOVLW

0x80

; Preload TMR1 register pair

MOVWF

TMR1H

; for 1 second overflow

CLRF

TMR1L

MOVLW

b'00001111'

; Configure for external clock,

MOVWF

T1CON

; Asynchronous operation, external oscillator

CLRF

secs

; Initialize timekeeping registers

CLRF

mins

;

MOVLW

.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

.59

; 60 seconds elapsed?

CPFSGT

secs

RETURN

; No, done

CLRF

secs

; Clear seconds

INCF

mins, F

; Increment minutes

MOVLW

.59

; 60 minutes elapsed?

CPFSGT

mins

RETURN

; No, done

CLRF

mins

; clear minutes

INCF

hours, F

; Increment hours

MOVLW

.23

; 24 hours elapsed?

CPFSGT

hours

RETURN

; No, done

MOVLW

.01

; Reset hours to 1

MOVWF

hours

RETURN

; Done