BS84B08A-3 Datasheet, PDF (45/123 Pages) Holtek Semiconductor Inc – A/D Type Touch Key MCU

BS84B08A-3/BS84C12A-3
A/D Type Touch Key MCU
Low Voltage Reset – LVR
The microcontroller contains a low voltage reset circuit in order to monitor the supply voltage of
the device, which is selected via a configuration option. 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.
For a valid LVR signal, a low voltage, i.e., a voltage in the range between 0.9V~ VLVR must exist
for greater than the value tLVR 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 VLVR is set by 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
Low Voltage Reset Timing Chart
LVRC Register
Bit
Name
R/W
POR
7
LVS7
R/W
0
6
LVS6
R/W
1
5
LVS5
R/W
0
4
LVS4
R/W
1
3
LVS3
—
0
2
LVS2
R/W
1
1
LVS1
R/W
0
0
LVS0
R/W
1
Bit 7~0
LVS7 ~ LVS0: LVR Voltage Select control
01010101: 2.55V(default)
00110011: 2.55V
10011001: 2.55V
10101010: 2.55V
Other values: MCU reset (reset will be active after 2~3 LIRC clock for debounce time)
Note: S/W can write 00H~FFH to control LVR voltage, even to S/W reset MCU. If
the MCU reset caused LVRC software reset, the LRF flag of CTRL register will be set.
Rev. 1.00
45
May 02, 2013