SyncMOS Technologies International, Inc.
SM894051
8-Bits Micro-controller
With 4KB Flash ROM embedded
I/O are provided with LED driving capacity
LEDEN (LEDENP1, 93H)
Bit7
LEDEN
P17
Bit6
LEDEN
P16
Bit5
LEDEN
P15
Bit4
LEDEN
P14
Bit3
LEDEN
P13
Bit2
LEDEN
P12
Bit1
LEDEN
P11
Bit0
LEDEN
P10
LEDEN (LEDENP3, 95H)
Bit7
LEDEN
P37
Bit6
Unused
Bit5
LEDEN
P35
Bit4
LEDEN
P34
Bit3
LEDEN
P33
Bit2
LEDEN
P32
Bit1
LEDEN
P31
Bit0
LEDEN
P30
When I/O Ports (Port1 & Port3) output low voltage, they are provided with more sink current (IIL about 20mA) to
drive LED by setting LED enable bit.
For example, when setting LEDNP1 [0] to high then P1.0 is provided with more sink current (IIL) to drive LED. And
so on, each I/O can be set to drive LED by setting correspondent register.
Extension Function Description
Watch Dog Timer
The Watch Dog Timer (WDT) is a 16-bits free-running counter that generate reset signal if the counter overflows.
The WDT is useful for systems that 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 of general 8051. 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 independent 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-bits 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 SM894051 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-bits counter and let the counter re-start to count from the beginning.
Watch Dog Timer Registers
Watch Dog Key Register
WDTKEY ($97)
Bit7
Bit6
Bit5
Bit4
Bit3
Bit2
Bit1
Bit0
WDT KEY7 WDT KEY6 WDT KEY5 WDT KEY4 WDT KEY3 WDT KEY2 WDT KEY1 WDT KEY0
By default, the WDTC is read only. User needs to write values 1EH, 0E1H sequentially to the WDTKEY (97H)
register to enable the WDTC write attribute, which is
MOV WDTKEY, # 01EH
MOV WDTKEY, # 0E1H
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, # 0E1H
MOV WDTKEY, # 01EH
Specifications subject to change without notice contact your sales representatives for the most recent information.
SM894051 V1.4 09 /2006
11
SYNCMOS [ SYNCMOS TECHNOLOGIES,INC ]
