PIC16CE623 datasheet(39/114 Pages) MICROCHIP

39 / 114 page

 1998-2013 Microchip Technology Inc.

DS40182D-page 39

PIC16CE62X

7.3.1

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 7-1) must be executed when changing the

prescaler assignment from Timer0 to WDT.

EXAMPLE 7-1:

CHANGING PRESCALER

(TIMER0

WDT)

1.BCF

STATUS, RP0

;Skip if already in

; Bank 0

2.CLRWDT

;Clear WDT

3.CLRF

TMR0

;Clear TMR0 & Prescaler

4.BSF

STATUS, RP0

;Bank 1

5.MOVLW

'00101111’b

;These 3 lines (5, 6, 7)

6.MOVWF

OPTION

; are required only if

; desired PS<2:0> are

7.CLRWDT

; 000 or 001

8.MOVLW

'00101xxx’b

;Set Postscaler to

9.MOVWF

OPTION

; desired WDT rate

10.BCF

STATUS, RP0

;Return to Bank 0

To change prescaler from the WDT to the TMR0

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

precaution must be taken even if the WDT is disabled.

EXAMPLE 7-2:

CHANGING PRESCALER

(WDT

TIMER0)

CLRWDT

;Clear WDT and

;prescaler

BSF

STATUS, RP0

MOVLW

b'xxxx0xxx'

;Select TMR0, new

;prescale value and

;clock source

MOVWF

OPTION_REG

BCF

STATUS, RP0

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

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

85h

TRISA

—

—TRISA4

TRISA3

TRISA2

TRISA1

TRISA0

---1 1111

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

Note:

Shaded bits are not used by TMR0 module.

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