PIC16LC71 datasheet(35/176 Pages) MICROCHIP

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DS30272A-page 35

PIC16C71X

6.3.1

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 6-1) 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 6-1:

CHANGING PRESCALER (TIMER0

→WDT)

BCF

STATUS, RP0

;Bank 0

CLRF

TMR0

;Clear TMR0 & Prescaler

BSF

STATUS, RP0

;Bank 1

CLRWDT

;Clears WDT

MOVLW

b'xxxx1xxx'

;Selects new prescale value

MOVWF

OPTION_REG

;and assigns the prescaler to the WDT

BCF

STATUS, RP0

;Bank 0

To change prescaler from the WDT to the Timer0

module use the sequence shown in Example 6-2.

EXAMPLE 6-2:

CHANGING PRESCALER (WDT

→TIMER0)

CLRWDT

;Clear WDT and prescaler

BSF

STATUS, RP0 ;Bank 1

MOVLW

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

MOVWF

OPTION_REG

;clock source

BCF

STATUS, RP0 ;Bank 0

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,

BOR

Value on all

other resets

01h

TMR0

Timer0 module’s register

xxxx xxxx

uuuu uuuu

0Bh,8Bh,

INTCON

GIE

ADIE

T0IE

INTE

RBIE

T0IF

INTF

RBIF

0000 000x

0000 000u

81h

OPTION RBPU INTEDG

T0CS

T0SE

PSA

PS2

PS1

PS0

1111 1111

85h

TRISA

—

PORTA Data Direction Register

---1 1111

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

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