SM8958A Datasheet, PDF (11/25 Pages) SyncMOS Technologies,Inc – 8 - Bit Micro-controller with 32KB flash & 1KB RAM embedded

SyncMOS Technologies Inc.
September 2002
SM8958A
3.Watch Dog Timer
The Watch Dog Timer (WDT) is a 16-bit free-running counter that generate reset signal if the counter overflows. The WDT is
useful for systems which are susceptible to noise, power glitches, or electronics discharge which causing software dead
loop or runaway. The WDT function can help user software recover from abnormal software condition. The WDT is different
from Timer0, Timer1 and Timer2 of general 8052. To prevent a WDT reset can be done by software periodically clearing the
WDT counter. User should check WDR bit of SCONF register whenever un-predicted reset happened
The purpose of the secure procedure is to prevent the WDTC value from being changed when system runaway.
There is a 250KHz RC oscillator embedded in chip. Set WDTE = “1” will enable the RC oscillator and the frequency is inde-
pendent to the system frequency.
To enable the WDT is done by setting 1 to the bit 7 (WDTE) of WDTC. After WDTE set to 1, the 16-bit counter starts to count
with the RC oscillator. It will generate a reset signal when overflows. The WDTE bit will be cleared to 0 automatically when
SM8958A been reset, either hardware reset or WDT reset.
To reset the WDT is done by setting 1 to the CLEAR bit of WDTC before the counter overflow. This will clear the content of
the 16-bit counter and let the counter re-start to count from the beginning.
3.1 Watch Dog Timer Registers:
Watch Dog Timer Registers - WDT Control Register (WDTC, $9F)
bit-7
bit-0
Read :
Write :
WDTE Unused CLEAR Unused Unused
PS2
PS1
PS0
Reset value :
0
*
0
*
*
0
0
0
WDTE : Watch Dog Timer enable bit
CLEAR : Watch Dog Timer reset bit
PS[2:0] : Overflow period select bits
PS [2:0]
000
001
010
011
100
101
110
111
Overflow Period (ms)
2.048
4.096
8.192
16.384
32.768
65.536
131.072
262.144
Specifications subject to change without notice,contact your sales representatives for the most recent information.
11/25
Ver 1.0 PID 8958A 09/02