PIC16F84A datasheet(69/337 Pages) MICROCHIP

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DS30234D-page 69

PIC16C6X

7.3.1

SWITCHING PRESCALER ASSIGNMENT

The prescaler assignment is fully under software con-

trol, i.e., it can be changed “on the ﬂy” during program

execution.

EXAMPLE 7-1:

CHANGING PRESCALER (TIMER0

→WDT)

To change prescaler from the WDT to the Timer0 mod-

ule, use the sequence shown in Example 7-2.

EXAMPLE 7-2:

CHANGING PRESCALER (WDT

→TIMER0)

CLRWDT

;Clear WDT and prescaler

BSF

STATUS, RP0 ;Bank 1

MOVLW

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

MOVWF

OPTION_REG

;

BCF

STATUS, RP0 ;Bank 0

TABLE 7-1:

REGISTERS ASSOCIATED WITH TIMER0

Note:

To avoid an unintended device RESET, the

following instruction sequence (shown in

Example 7-1) must be executed when

changing the prescaler assignment from

Timer0 to the WDT. This precaution must

be followed even if the WDT is disabled.

BSF

STATUS, RP0

;Bank 1

Lines 2 and 3 do NOT have to

be included if the ﬁnal desired

prescale value is other than 1:1.

If 1:1 is ﬁnal desired value, then

a temporary prescale value is

set in lines 2 and 3 and the ﬁnal

prescale value will be set in lines

10 and 11.

MOVLW

b'xx0x0xxx'

;Select clock source and prescale value of

MOVWF

OPTION_REG

;other than 1:1

BCF

STATUS, RP0

;Bank 0

CLRF

TMR0

;Clear TMR0 and prescaler

BSF

STATUS, RP1

;Bank 1

MOVLW

b'xxxx1xxx'

;Select WDT, do not change prescale value

MOVWF

OPTION_REG

;

CLRWDT

;Clears WDT and prescaler

10) MOVLW

b'xxxx1xxx'

;Select new prescale value and WDT

11) MOVWF

OPTION_REG

;

12) BCF

STATUS, RP0

;Bank 0

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, 101h

TMR0

Timer0 module’s register

xxxx xxxx

uuuu uuuu

0Bh,8Bh,

10Bh,18Bh

INTCON

GIE

PEIE(1)

T0IE

INTE

RBIE

T0IF

INTF

RBIF

0000 000x

0000 000u

81h, 181h

OPTION RBPU INTEDG

T0CS

T0SE

PSA

PS2

PS1

PS0

1111 1111

85h

TRISA

—

PORTA Data Direction Register

(1)

--11 1111

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

Note 1:

TRISA<5> and bit PEIE are not implemented on the PIC16C61, read as '0'.

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