Datasheet

 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 1111 1111
85h TRISA
— — —TRISA4TRISA3 TRISA2 TRISA1 TRISA0 ---1 1111 ---1 1111
Legend: — = Unimplemented locations, read as ‘0’, x = unknown, u = unchanged.
Note: Shaded bits are not used by TMR0 module.