Datasheet

 1997 Microchip Technology Inc. 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 1111 1111
85h TRISA — — — PORTA Data Direction Register ---1 1111 ---1 1111
Legend: x = unknown, u = unchanged, - = unimplemented locations read as '0'. Shaded cells are not used by Timer0.