W79E648 Datasheet, PDF (51/80 Pages) Winbond – Fast 8051 Compatible microcontroller with a redesigned Processor

Preliminary W79E648
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 time is 512 clock longer than the interrupt
time-out value.
The default Watchdog time-out is 2¹⁷ clocks, which is the shortest time-out period. The EWT, WDIF
and RWT bits are protected by the Timed Access procedure. This prevents software from accidentally
enabling or disabling the watchdog timer. More importantly, it makes it highly improbable that errant
code can enable or disable the watchdog timer. Please refer as below demo program.
org 63h
mov TA,#AAH
mov TA,#55H
clr WDIF
jnb execute_reset_flag,bypass_reset
jmp $
bypass_reset:
mov TA,#AAH
mov TA,#55H
setb RWT
reti
; Test if CPU need to reset.
; Wait to reset
start:
;
;
;
org 300h
mov ckcon,#01h ; select 2 ^ 17 timer
mov ckcon,#61h ; select 2 ^ 20 timer
mov ckcon,#81h ; select 2 ^ 23 timer
mov ckcon,#c1h ; select 2 ^ 26 timer
mov TA,#aah
mov TA,#55h
mov WDCON,#00000011B
setb EWDI
setb ea
jmp $
; wait time out
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Publication Release Date: 05/31/2004
Revision A1