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CHAPTER 4 I/O PORTS
4.5 Port 3
Port 3 is N-ch open-drain I/O port. Two of them also serve as LCD bias input. Port 3 pins
can be switched between LCD bias input and port operation. This section principally
describes the port functions when operating as N-ch open-drain I/O port.
The section describes the port structure and pins, the pin block diagram, and the port
register for port 3.
■ Structure of port 3
Port 3 consists of the following two components:
• N-ch open-drain I/O pins/LCD bias input pins (P30 to P33/V2)
• Port 3 data register (PDR3)
■ Port 3 pins
Port 3 consists of four N-ch open-drain I/O. When pins are used by the peripheral, they cannot be used as
N-ch open-drain I/O.
Table 4.5-1 "Port 3 pins" lists the port 3 pins.
See Section 1.7 "I/O Pins and Pin Functions" for a description of the circuit type.
Table 4.5-1 Port 3 pins
Port Pin name Function Shared peripheral
I/O type
Circuit
type
Input Output
Port 3
P30 P30 N-ch open-drain I/O --
CMOS N-ch open-drain F
P31 P31 N-ch open-drain I/O --
P32/V1 P32 N-ch open-drain I/O V1 LCD bias input
LCD bias/CMOS N-ch open-drain H
P33/V2 P33 N-ch open-drain I/O V2 LCD bias input