W79E225A_08 Datasheet, PDF (106/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A Data Sheet
The POR, EWT, WDIF and RWT bits are protected by the Timed Access procedure. This procedure
prevents software, especially errant code, from accidentally enabling or disabling the Watchdog Timer.
An example is provided below.
org
mov
mov
clr
jnb
jmp
bypass_reset:
mov
mov
setb
reti
63h
TA,#AAH
TA,#55H
WDIF
execute_reset_flag,bypass_reset
$
TA,#AAH
TA,#55H
RWT
; Test if CPU need to reset.
; Wait to reset
org
start:
mov
;
mov
;
mov
;
mov
mov
mov
mov
setb
setb
jmp
300h
ckcon,#01h
ckcon,#61h
ckcon,#81h
ckcon,#c1h
TA,#aah
TA,#55h
WDCON,#00000011B
EWDI
ea
$
; Select 2 ^ 17 timer
; Select 2 ^ 20 timer
; Select 2 ^ 23 timer
; Select 2 ^ 26 timer
; Wait time out
Clock Control
WD1, WD0: CKCON.7, CKCON.6 - Watchdog Timer Mode select bits. These two bits select the time-
out interval for the Watchdog Timer. The reset interval is 512 clocks longer than the selected interval.
The default time-out is 2¹⁷ clocks, the shortest time-out period.
- 106 -
Publication Release Date: April 15, 2008
Revision A4.0