SyncMOS Technologies Inc.
January 2003
Preliminary
SM79108
Addr
0E2H
0E3H
0E4H
0E5H
0E6H
0E7H
SFR
LCDB1
LCDB2
LCDB3
LCDB4
LCDB5
LCDB6
Reset
00H
00H
00H
00H
00H
00H
7
SEG2
SEG4
SEG6
SEG8
SEG10
SEG12
6
SEG2
SEG4
SEG6
SEG8
SEG10
SEG12
5
SEG2
SEG4
SEG6
SEG8
SEG10
SEG12
4
SEG2
SEG4
SEG6
SEG8
SEG10
SEG12
3
SEG3
SEG5
SEG7
SEG9
SEG11
SEG13
2
SEG3
SEG5
SEG7
SEG9
SEG11
SEG13
1
SEG3
SEG5
SEG7
SEG9
SEG11
SEG13
0
SEG3
SEG5
SEG7
SEG9
SEG11
SEG13
1. 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 unpracticed 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
SM79108 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.
1.1 Watch Dog Timer Registers:
Watch Dog Key Register - (WDTKEY, 97H)
bit-7
WDT
KEY7
Read / Write:
Reset value:
W
0
WDT
KEY6
W
0
WDT
KEY5
W
0
WDT
KEY4
W
0
WDT
KEY3
W
0
WDT
KEY2
W
0
WDT
KEY1
W
0
bit-0
WDT
KEY0
W
0
By default, the WDTC is read only. User need to write values 1EH, 0E1H sequentially to the WDTKEY(97H) register to
enable the WDTC write attribute, That is
MOV WDTKEY, # 1EH
MOV WDTKEY, # E1H
When WDTC is set, user need to write another values E1H, 1EH sequentially to the WDTKEY(97H) register to disable the
WDTC write attribute, That is
MOV WDTKEY, # E1H
MOV WDTKEY, # 1EH
Specifications subject to change without notice,contact your sales representatives for the most recent information.
6/26
Preliminary
Ver 1.0
SM79108 01/03
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
