Datasheet

PIC16F5X
DS41213D-page 36 © 2007 Microchip Technology Inc.
7.2.1 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 the WDT.
EXAMPLE 7-1: CHANGING PRESCALER
(TIMER0→WDT)
To change prescaler from the WDT to the Timer0
module, use the sequence shown in Example 7-2. This
sequence must be used even if the WDT is disabled. A
CLRWDT instruction should be executed before
switching the prescaler.
EXAMPLE 7-2: CHANGING PRESCALER
(WDT→TIMER0)
FIGURE 7-5: BLOCK DIAGRAM OF THE TIMER0/WDT PRESCALER
CLRWDT ;Clear WDT
CLRF TMR0 ;Clear TMR0 & ;Prescaler
MOVLW B'00xx1111’ ;Last 3 instructions
;in this example
OPTION ;are required only if
;desired
CLRWDT ;PS<2:0> are 000 or 001
MOVLW B'00xx1xxx’ ;Set Prescaler to
OPTION ;desired WDT rate
CLRWDT ;Clear WDT and
;prescaler
MOVLW B'xxxx0xxx' ;Select TMR0, new
;prescale value and
;clock source
OPTION
T0CKI
T0SE
(1)
pin
TCY ( = FOSC/4)
Sync
2
Cycles
TMR0 reg
8-bit Prescaler
8-to-1 MUX
M
MUX
Watchdog
Timer
PSA
(1)
0
1
0
1
WDT
Time-Out
PS<2:0>
(1)
8
PSA
(1)
WDT Enable bit
0
1
0
1
Data Bus
8
PSA
(1)
T0CS
(1)
M
U
X
M
U
X
U
X
Note 1: T0CS, T0SE, PSA PS<2:0> are bits in the Option register.