PIC16LC74AT-04I/SP 查看數據表（PDF） - Microchip Technology

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PIC16LC74AT-04I/SP

8-Bit CMOS Microcontrollers with A/D Converter

Microchip Technology 

PIC16C7X

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 sequence 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)

be included if the final desired 3)

prescale value is other than 1:1. 4)

If 1:1 is final desired value, then

a temporary prescale value is 5)

set in lines 2 and 3 and the final 6)

prescale value will be set in lines 7)

10 and 11.

8)

MOVLW

MOVWF

BCF

CLRF

BSF

MOVLW

MOVWF

b'xx0x0xxx'

OPTION_REG

STATUS, RP0

TMR0

STATUS, RP1

b'xxxx1xxx'

OPTION_REG

9) CLRWDT

10) MOVLW b'xxxx1xxx'

11) MOVWF OPTION_REG

12) BCF STATUS, RP0

;Bank 1

;Select clock source and prescale value of

;other than 1:1

;Bank 0

;Clear TMR0 and prescaler

;Bank 1

;Select WDT, do not change prescale value

;

;Clears WDT and prescaler

;Select new prescale value and WDT

;

;Bank 0

To change prescaler from the WDT to the Timer0 mod-

ule use the sequence shown in Example 7-2.

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

CLRWDT

BSF

MOVLW

MOVWF

BCF

;Clear WDT and prescaler

STATUS, RP0 ;Bank 1

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

OPTION_REG ;clock source

STATUS, RP0 ;Bank 0

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:

POR,

BOR

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 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.

DS30390E-page 63

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