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CHAPTER 22 RESET FUNCTION
User’s Manual U12790EJ2V0UD
22.3 4.5 V Voltage Detection Function
This function is used to detect a voltage drop on the VDD pin below 4.5 V (4.5 V
± 0.3 V). If the voltage on the
VDD pin drops below 4.5 V (4.5 V
± 0.3 V), bit 1 (VM45) of the POC status register (POCS) is set. At the same time,
this status can be monitored by the VM45/P30 pin. Therefore, the power to the other peripheral units can be controlled
when a voltage of less than 4.5 V is detected.
Note, however, that this 4.5 V voltage detection function does not cause an internal reset.
Figure 22-6. Format of POC Status Register (POCS)
VM45
Detection of voltage level of VDD pin
0
Not detected if VDD pin is less than 4.5 V (4.3
± 0.3 V)
1
Detected if VDD pin is less than 4.5 V (4.3
± 0.3 V)
Note
The value of this register is set to 03H only at power-on clear reset, and is not reset by the RESET
pin or watchdog timer.
Remark
The values of the special-function registers other than POCS after reset are the same as the values
at power-on clear.
The status detected (not detected) by VM45 can be output to (monitored by) the VM45/P30 pin under control of
the VM45 control register (VM45C).
Figure 22-7. Format of VM45 Control Register (VM45C)
VM45C1
Enable/disable of output of VM45 (VDD 4.5 V monitor)
0
Output of VM45 to VM45/P30 pin disabled (port function)
1Note
Output of VM45 to VM45/P30 pin enabled
VM45C0
Selection of output of VM45 (VDD 4.5 V monitor)
0
High level output
1
Low level output
Note
When the VM45/P30 pin is used for VM45 output, reset the output latches of bit 0 (PM30) of PM3 and
bit 0 (P30) of P3 to 0.
7
0
6
0
5
0
4
0
3
0
2
0
VM45C1
Symbol
VM45C
After reset
00H
R/W
VM45C0
<0>
<1>
Address
FF19H
7
0
6
0
5
0
4
0
3
0
2
0
1
VM45
0
POCM
Symbol
POCS
After reset
Held
Note
R/W
R&Reset
Address
FF1BH