PIC16C621A Microchip Technology Inc., PIC16C621A Datasheet - Page 37

• Manufacturer Part Number: PIC16C621A
• Description: Eprom-based 8-bit Cmos Microcontrollers
• Manufacturer: Microchip Technology Inc.

6.3.1
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,
(Example 6-1) must be executed when changing the
prescaler assignment from Timer0 to WDT.)
EXAMPLE 6-1:
TABLE 6-1:
 2003 Microchip Technology Inc.
10.BCF
Address Name
01h
0Bh/8Bh
81h
85h
Legend: — = Unimplemented locations, read as ‘0’, u = unchanged, x = unknown
1.BCF
2.CLRWDT
3.CLRF
4.BSF
5.MOVLW
6.MOVWF
7.CLRWDT
8.MOVLW
9.MOVWF
Note:
the
SWITCHING PRESCALER
ASSIGNMENT
TMR0
INTCON
OPTION
TRISA
Shaded bits are not used by TMR0 module.
STATUS, RP0
TMR0
STATUS, RP0
'00101111’b;
OPTION
'00101xxx’b
OPTION
STATUS, RP0
REGISTERS ASSOCIATED WITH TIMER0
following
Bit 7
Timer0 module register
RBPU
CHANGING PRESCALER
(TIMER0→WDT)
GIE
—
;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
Bit 6
INTEDG
instruction
PEIE
—
Bit 5
T0CS
T0IE
—
sequence
Bit 4
TRISA4
T0SE
INTE
Bit 3
TRISA3
RBIE
PSA
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:
BSF
MOVLW
MOVWF
BCF
CLRWDT
Bit 2
TRISA2
T0IF
PS2
Bit 1
TRISA1
INTF
STATUS, RP0
PS1
STATUS, RP0
b'xxxx0xxx'
OPTION_REG
Bit 0
TRISA0 ---1 1111 ---1 1111
RBIF
PS0
CHANGING PRESCALER
(WDT→TIMER0)
PIC16C62X
Value on
POR
xxxx xxxx uuuu uuuu
0000 000x 0000 000u
1111 1111 1111 1111
;Select TMR0, new
;Clear WDT and
;prescaler
;prescale value and
;clock source
DS30235J-page 35
Value on
All Other
RESETS