71

Chapter 5 Port Functions
5

Fig. 5-13 Block Diagram of P33 (Port 3)

5.4.2 Setting the I/O Mode and Control Mode

The port 3 mode register (PM3) can put each pin of port 3 in either the input or output mode independently of the

other pins, as shown in Fig. 5-14.

The PM3 register is loaded with data using an 8-bit data transfer instruction; it cannot be bit-manipulated or read-

accessed.

In addition to I/O port functions, each pin of port 3 works as a control signal pin. As shown in Fig. 5-15, the port

3 mode control register (PMC3) can specify the mode of control for each pin.

Internal bus
RDOUT
P33
VDD
RDIN
RDPUO
WRPUO Pull-up resistor option register
PUO3
WRPM33 Port 3 mode register
PM33
WRPMC33
PMC33
RDPMC33
WRP33
P33
Selector
Output latch
SB0 output
SO output
PMC33
Output disable
Output
disable
SBI mode
PMC33
SB0 input