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(2) Pull-up resistor option register (PUO)
The PUO register enables or disables the on-chip pull-up resistor for each port pin. To enable the on-chip pull-
up resistor of a port pin, the pin must be in the input mode and the corresponding bit in the PUO register must
be set to 1. For any pin specified as output mode or used as an analog input pin, the on-chip pull-up resistors
cannot be used, regardless of the PUO register setting.
PUO is set with a 1-bit or 8-bit memory manipulation instruction.
RESET input sets this register to 00H.
Cautions 1. The P00 and P04 pins do not incorporate a pull-up resistor.
2. When port 1 is used as analog input for the A/D converter, an on-chip pull-up resistor cannot
be used even if 1 is set in PUO1.
Symbol
7
6
PUO
0
0
CHAPTER 4 PORT FUNCTIONS
Figure 4-15. Format of Pull-up Resistor Option Register
<3>
<2>
5
4
0
0
PUO3 PUO2 PUO1 PUO0
User's Manual U11302EJ4V0UM
Address
<1>
<0>
FFF7H
Pm on-chip pull-up resistor selection
PUOm
(m = 0, 1, 2, 3)
0
On-chip pull-up resistor not used
1
On-chip pull-up resistor used
After reset
R/W
00H
R/W
97
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