PIC16F628-20P Datasheet, PDF (47/170 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontroller

PIC16F62X
6.3.1
SWITCHING PRESCALER
ASSIGNMENT
The prescaler assignment is fully under software
control (i.e., it can be changed “on the fly” during
program execution). Use the instruction sequences,
shown in Example 6-1, when changing the prescaler
assignment from Timer0 to WDT, to avoid an
unintended device RESET.
EXAMPLE 6-1:
CHANGING PRESCALER
(TIMER0→WDT)
BCF
CLRWDT
CLRF
BSF
MOVLW
MOVWF
CLRWDT
MOVLW
MOVWF
BCF
STATUS, RP0
TMR0
STATUS, RP0
'00101111’b
OPTION_REG
'00101xxx’b
OPTION_REG
STATUS, RP0
;Skip if already in
;Bank 0
;Clear WDT
;Clear TMR0 & Prescaler
;Bank 1
;These 3 lines
;(5, 6, 7)
;are required only
;if desired PS<2:0>
;are
;000 or 001
;Set Postscaler to
;desired WDT rate
;Return to Bank 0
To change prescaler from the WDT to the TMR0
module use the sequence shown in Example 6-2. This
precaution must be taken even if the WDT is disabled.
EXAMPLE 6-2:
CHANGING PRESCALER
(WDT→TIMER0)
CLRWDT
BSF
MOVLW
MOVWF
BCF
STATUS, RP0
b'xxxx0xxx'
OPTION_REG
STATUS, RP0
;Clear WDT and
;prescaler
;Select TMR0, new
;prescale value and
;clock source
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
Value on
All Other
RESETS
01h
TMR0
0Bh/8Bh/
10Bh/18Bh
INTCON
Timer0 module register
GIE
PEIE T0IE
INTE
RBIE
T0IF
INTF
xxxx xxxx uuuu uuuu
RBIF 0000 000x 0000 000u
81h, 181h _OPTION⁽²⁾ RBPU INTEDG T0CS T0SE PSA
PS2
PS1
PS0 1111 1111 1111 1111
85h
TRISA
TRISA7 TRISA6 TRISA5 TRISA4 TRISA3 TRISA2 TRISA1 TRISA0 1111 1111 1111 1111
Legend: — = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown
Note 1: Shaded bits are not used by TMR0 module.
2: Option is referred by OPTION_REG in MPLAB.
 2003 Microchip Technology Inc.
Preliminary
DS40300C-page 45