PIC16C558T-IL View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16C558T-IL

EPROM-Based 8-Bit CMOS Microcontrollers

Microchip Technology 

PIC16C55X

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. Lines 5-7

are required only if the desired postscaler rate is 1:1

(PS<2:0> = 000) or 1:2 (PS<2:0> = 001).

EXAMPLE 7-1: CHANGING PRESCALER

(TIMER0WDT)

BCF STATUS, RP0 ;Skip if already in

;Bank 0 CLRWDT Clear WDT

CLRF TMR0

;Clear TMR0 & Prescaler

BSF STATUS, RP0 ;Bank 1

MOVLW '00101111’b ;These 3 lines (5, 6, 7)

MOVWF OPTION

;Are required only if

;Desired PS<2:0> are

;CLRWDT 000 or 001

MOVLW '00101xxx’b ;Set Postscaler to

MOVWF OPTION

;Desired WDT rate

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

BSF

MOVLW

MOVWF

BCF

STATUS, RP0

b'xxxx0xxx'

OPTION

STATUS, RP0

;Clear WDT and 

;prescaler

;Select TMR0, new 

;prescale value and

;clock source

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

01h

TMR0 Timer0 module’s register

0Bh/8Bh INTCON GIE Reserved T0IE

81h

OPTION RBPU INTEDG T0CS

85h

TRISA

—

—

—

Legend: — = Unimplemented locations, read as ‘0’,

Note 1: Shaded bits are not used by TMR0 module.

INTE

T0SE

TRISA4

RBIE

PSA

TRISA3

T0IF

PS2

TRISA2

INTF

PS1

TRISA1

RBIF

PS0

TRISA0

Value on

POR

xxxx xxxx

0000 000x

1111 1111

---1 1111

Value on

All Other

RESETS

uuuu uuuu

0000 000x

1111 1111

---1 1111

 1996-2013 Microchip Technology Inc.

Preliminary

DS40143E-page 51

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