PIC16C620AT-20 查看數據表（PDF） - Microchip Technology

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PIC16C620AT-20

EPROM-Based 8-Bit CMOS Microcontrollers

Microchip Technology 

6.3.1

SWITCHING PRESCALER

ASSIGNMENT

The prescaler assignment is fully under software

control (i.e., it can be changed “on-the-fly” during

program execution). To avoid an unintended device

RESET, the following instruction sequence

(Example 6-1) must be executed when changing the

prescaler assignment from Timer0 to WDT.)

EXAMPLE 6-1:

CHANGING PRESCALER

(TIMER0→WDT)

1.BCF

2.CLRWDT

3.CLRF

4.BSF

5.MOVLW

6.MOVWF

7.CLRWDT

8.MOVLW

9.MOVWF

10.BCF

STATUS, RP0

TMR0

STATUS, RP0

'00101111’b;

OPTION

'00101xxx’b

OPTION

STATUS, RP0

;Skip if already in

;Bank 0

;Clear WDT

;Clear TMR0 & Prescaler

;Bank 1

;These 3 lines (5, 6, 7)

;are required only if

;desired PS<2:0> are

;000 or 001

;Set Postscaler to

;desired WDT rate

;Return to Bank 0

PIC16C62X

To change prescaler from the WDT to the TMR0

module, use the sequence shown in Example 6-2. This

precaution must be taken even if the WDT is disabled.

EXAMPLE 6-2:

CHANGING PRESCALER

(WDT→TIMER0)

CLRWDT

BSF

MOVLW

STATUS, RP0

b'xxxx0xxx'

MOVWF

BCF

OPTION_REG

STATUS, RP0

;Clear WDT and

;prescaler

;Select TMR0, new

;prescale value and

;clock source

TABLE 6-1: 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

Value on

All Other

RESETS

01h

TMR0 Timer0 module register

xxxx xxxx uuuu uuuu

0Bh/8Bh INTCON GIE PEIE T0IE INTE RBIE T0IF INTF RBIF 0000 000x 0000 000u

81h

OPTION RBPU INTEDG T0CS T0SE PSA

PS2

PS1

PS0 1111 1111 1111 1111

85h

TRISA

—

—

— TRISA4 TRISA3 TRISA2 TRISA1 TRISA0 ---1 1111 ---1 1111

Legend: — = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown

Note: Shaded bits are not used by TMR0 module.

 2003 Microchip Technology Inc.

DS30235J-page 35

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