Rev. 1.71
48
April 11, 2017
Rev. 1.71
49
April 11, 2017
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
HT66F002/HT66F0025/HT66F003/HT66F004
Cost-Effective A/D Flash MCU with EEPROM
SMOD1 Register
Bit
7
6
5
4
3
2
1
0
Name
FSYSON
—
—
—
D3
LVRF
—
WRF
R/W
R/W
—
—
—
R/W
R/W
—
R/W
POR
0
—
—
—
0
x
—
0
“x” unknown
B
it 7
FSYSON
: f
SYS
Control in IDLE Mode
0: Disable
1: Enable
Bit 6~4
Unimplemented, read as 0
Bit
3
D3
: Reserved bit
B
it 2
LVRF
: LVR function reset flag
0: Not active
1: Active
This bit can be clear to “0”, but can not be set to “1”.
B
it 1
Unimplemented, read as 0
B
it 0
WRF
: WDT Control register software reset flag
0: Not occur
1: Occurred
This bit is set to 1 by the WDT Control register software reset and cleared by the application program.
Note that this bit can only be cleared to 0 by the application program.
Watchdog Timer Operation
The Watchdog Timer operates by providing a device reset when its timer overflows. This means
that in the application program and during normal operation the user has to strategically clear the
Watchdog Timer before it overflows to prevent the Watchdog Timer from executing a reset. This is
done using the clear watchdog instructions. If the program malfunctions for whatever reason, jumps
to an unknown location, or enters an endless loop, the clear WDT instructions will not be executed
in the correct manner, in which case the Watchdog Timer will overflow and reset the device. With
regard to the Watchdog Timer enable/disable function, there are five bits, WE4~WE0, in the WDTC
register to additional enable/disable and reset control of the Watchdog Timer.
WE4 ~ WE0 Bits
WDT Function
10101B
Disable
01010B
Enable
Any other value
Reset MCU
Watchdog Timer Enable/Disable Control
Under normal program operation, a Watchdog Timer time-out will initialise a device reset and set
the status bit TO. However, if the system is in the SLEEP or IDLE Mode, when a Watchdog Timer
time-out occurs, the TO bit in the status register will be set and only the Program Counter and Stack
Pointer will be reset. Four methods can be adopted to clear the contents of the Watchdog Timer.
The first is a WDT reset, which means a value other than 01010B and 10101B is written into the
WE4~WE0 bit locations, the second is an external hardware reset, which means a low level on the
external reset pin, the third is using the Watchdog Timer software clear instructions and the fourth
is via a HALT instruction. There is only one method of using software instruction to clear the
Watchdog Timer. That is to use the single “CLR WDT” instruction to clear the WDT.