HT45F4M
Lithium Battery Backup Power ASSP MCU
Low Voltage Reset – LVR
The microcontroller contains a low voltage reset circuit in order to monitor the supply voltage of the
device. The LVR function is always enabled with a specific LVR voltage, VLVR. If the supply voltage
of the device drops to within a range of 0.9V~VLVR such as might occur when changing the battery,
the LVR will automatically reset the device internally and the LVRF bit in the CTRL register will
also be set to 1. For a valid LVR signal, a low supply voltage, i.e., a voltage in the range between
0.9V~VLVR must exist for a time greater than that specified by tLVR in the A.C. characteristics. If the
low supply voltage state does not exceed this value, the LVR will ignore the low supply voltage
and will not perform a reset function. The actual VLVR is fixed at a voltage value of 2.55V by the
LVS bits in the LVRC 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 CTRL 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.
LV R
tR S T D + tS S T
In te rn a l R e s e t
Note:tRSTD is power-on delay, typical time=16.7ms
Low Voltage Reset Timing Chart
• LVRC Register
Bit
7
Name LVS7
R/W
R/W
POR
0
6
LVS6
R/W
1
5
LVS5
R/W
0
4
LVS4
R/W
1
3
LVS3
R/W
0
2
LVS2
R/W
1
1
LVS1
R/W
0
0
LVS0
R/W
1
Bit 7 ~ 0
LVS7 ~ LVS0: LVR voltage select
01010101: 2.55V
00110011: 2.55V
10011001: 2.55V
10101010: 2.55V
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.
Rev. 1.10
44
January 15, 2013