PIC16C924-04 View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16C924-04

8-Bit CMOS Microcontroller with LCD Driver

Microchip Technology 

PIC16C9XX

7.3.1 SWITCHING PRESCALER ASSIGNMENT

The prescaler assignment is fully under software con-

trol, i.e., it can be changed “on the fly” during program

execution.

Note:

To avoid an unintended device RESET, the

following instruction sequence (shown in

Example 7-1) must be executed when

changing the prescaler assignment from

Timer0 to the WDT. This precaution must

be followed even if the WDT is disabled.

EXAMPLE 7-1: CHANGING PRESCALER (TIMER0→WDT)

1) BSF STATUS, RP0

Lines 2 and 3 do NOT have to 2) MOVLW b'xx0x0xxx'

be included if the final desired 3) MOVWF OPTION_REG

prescale value is other than 1:1. 4) BCF

If 1:1 is final desired value, then

a temporary prescale value is 5) CLRF

set in lines 2 and 3 and the final 6) BSF

STATUS, RP0

TMR0

STATUS, RP1

prescale value will be set in lines 7) MOVLW b'xxxx1xxx'

10 and 11.

8) MOVWF OPTION_REG

9) CLRWDT

10) MOVLW b'xxxx1xxx'

11) MOVWF OPTION_REG

12) BCF STATUS, RP0

;Select Bank1

;Select clock source and prescale value of

;other than 1:1

;Select Bank0

;Clear TMR0 and prescaler

;Select Bank1

;Select WDT, do not change prescale value

;

;Clears WDT and prescaler

;Select new prescale value and WDT

;

;Select Bank0

To change prescaler from the WDT to the Timer0 mod-

ule use the precaution shown in Example 7-2.

EXAMPLE 7-2: CHANGING PRESCALER (WDT→TIMER0)

CLRWDT

BSF

MOVLW

MOVWF

BCF

;Clear WDT and prescaler

STATUS, RP0 ;Select Bank1

b'xxxx0xxx' ;Select TMR0, new prescale value and

OPTION_REG ;clock source

STATUS, RP0 ;Select Bank0

TABLE 7-1: REGISTERS ASSOCIATED WITH TIMER0

Address Name Bit 7 Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on

Power-on

Reset

Value on all

other resets

01h, 101h TMR0 Timer0 module’s register

xxxx xxxx uuuu uuuu

0Bh, 8Bh, INTCON GIE

10Bh, 18Bh

PEIE

T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 000u

81h, 181h OPTION RBPU INTEDG T0CS T0SE PSA PS2 PS1 PS0 1111 1111 1111 1111

85h

TRISA

—

— PORTA Data Direction Control Register

--11 1111 --11 1111

Legend: x = unknown, u = unchanged, - = unimplemented locations read as '0'. Shaded cells are not used by Timer0.

© 1997 Microchip Technology Inc.

DS30444E - page 49

Share Link: