PIC16F54T-I/SO View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16F54T-I/SO

Flash-Based, 8-Bit CMOS Microcontroller Series

Microchip Technology 

PIC16F5X

7.2.1

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 7-1) must be

executed when changing the prescaler assignment

from Timer0 to the WDT.

EXAMPLE 7-1:

CHANGING PRESCALER

(TIMER0→WDT)

CLRWDT

CLRF

MOVLW

OPTION

CLRWDT

MOVLW

OPTION

TMR0

B'00xx1111’

B'00xx1xxx’

;Clear WDT

;Clear TMR0 & ;Prescaler

;Last 3 instructions

;in this example

;are required only if

;desired

;PS<2:0> are 000 or 001

;Set Prescaler to

;desired WDT rate

To change prescaler from the WDT to the Timer0

module, use the sequence shown in Example 7-2. This

sequence must be used even if the WDT is disabled. A

CLRWDT instruction should be executed before

switching the prescaler.

EXAMPLE 7-2:

CHANGING PRESCALER

(WDT→TIMER0)

CLRWDT

MOVLW

OPTION

B'xxxx0xxx'

;Clear WDT and

;prescaler

;Select TMR0, new

;prescale value and

;clock source

FIGURE 7-5:

BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER

TCY ( = FOSC/4)

T0CKI

pin

T0SE(1)

0

M

U

1X

T0CS(1)

1

M

U

0X

PSA(1)

Sync

2

Cycles

Data Bus

8

TMR0 reg

Watchdog

Timer

WDT Enable bit

0

M

U

1X

PSA(1)

8-bit Prescaler

8

8-to-1 MUX

PS<2:0>(1)

0

1

MUX

PSA(1)

WDT

Time-Out

Note 1: T0CS, T0SE, PSA PS<2:0> are bits in the Option register.

DS41213D-page 36

© 2007 Microchip Technology Inc.

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