Single-Chip Microcontrollers User's Manual

137

CHAPTER 6 PORT FUNCTIONS

6.2.5 Port 3

Port 3 is an 8-bit input/output port with output latch. P30 to P37 pins can specify the input mode/output mode in

1-bit units with the port mode register 3 (PM3). When P30 to P37 pins are used as input ports, an on-chip pull-up

resistor can be used to them in 8-bit units with a pull-up resistor option register L (PUOL).

Alternate functions include timer input/output, clock output, and buzzer output.

RESET input sets port 3 to input mode.

Figure 6-9 shows a block diagram of port 3.

Figure 6-9. P30 to P37 Block Diagram

PUO : Pull-up resistor option register

PM : Port mode register

RD : Port 3 read signal

WR : Port 3 write signal

P-ch

PORT

PUO

Selector

PUO3

Output Latch

(P30 to P37)

PM30 to PM37

Internal bus

Alternate Function

P30/TO0

P32/TO2,

P33/TI1,

P34/TI2,

P35/PCL,

P36/BUZ,

P37