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Rev. 1.00
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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Reset and Initialisation
Low Voltage Reset – LVR
The microcontroller contains a low voltage reset circuit in order to monitor the supply voltage of
the device and provide an MCU reset should the value fall below a certain predefined level.
The LVR function is always enabled with a specific LVR voltage, V
LVR
. If the supply voltage of
the device drops to within a range of 0.9V~V
LVR
such as might occur when changing the battery
in battery powered applications, the LVR will automatically reset the device internally and the
LVRF bit in the RSTSRC register will also be set to1. For a valid LVR signal, a low voltage, i.e., a
voltage in the range between 0.9V~V
LVR
must exist for greater than the value t
LVR
specified in the
A.C. characteristics. If the low voltage state does not exceed this value, the LVR will ignore the
low supply voltage and will not perform a reset function. The actual V
LVR
value can be selected by
the LVSn bits in the LVRCR register. If the LVS7~LVS0 bits are changed to some certain values
by the environmental noise, the LVR will reset the device after 2~3 LIRC clock cycles. When this
happens, the LRF bit in the RSTSRC register will be set to 1. After power on the register will have
the value of 01010101B. Note that the LVR function will be automatically disabled when the device
enters the power-down mode.
LVRCR Register
SFR Address: EAh
Bit
7
6
5
4
3
2
1
0
Name
LVS7
LVS6
LVS�
LVS4
LVS3
LVS�
LVS1
LVS0
R/W
R/W
R/W
R/W
R/W
R
R
R/W
R/W
POR
0
1
0
1
0
1
0
1
Bit 7~0
LVS7~LVS0:
LVR Voltage Select control
01010101: 2.1V
00110011: 2.55V
10011001: 3.15V
10101010: 4.0V
Any other value: Generates MCU reset – register is reset to POR value
When an actual low voltage condition occurs, as specified by the above defined LVR
voltage value, an MCU reset will be generated. The reset operation will be activated
after 2~3 LIRC clock cycles. In this situation this register contents will remain the same
after such a reset occurs.
Any register value, other than the four defined values above, will also result in the
generation of an MCU reset. The reset operation will be activated after 2~3 LIRC clock
cycles. However in this situation this register contents will be reset to the POR value.