Datasheet

 1997-2013 Microchip Technology Inc. DS30234E-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.
1) 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.
2) MOVLW b'xx0x0xxx' ;Select clock source and prescale value of
3) MOVWF OPTION_REG ;other than 1:1
4) BCF STATUS, RP0 ;Bank 0
5) CLRF TMR0 ;Clear TMR0 and prescaler
6) BSF STATUS, RP1 ;Bank 1
7) MOVLW b'xxxx1xxx' ;Select WDT, do not change prescale value
8) MOVWF OPTION_REG ;
9) 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 1111 1111
85h TRISA
— —
PORTA Data Direction Register
(1)
--11 1111 --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'.