CHAPTER 14 PORT FUNCTION
User’s Manual U13850EJ4V0UM
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(1) Function of P3 pins
Port 3 is an 8-bit I/O port for which I/O settings can be controlled in 1-bit units. I/O settings are controlled via the
port 3 mode register (PM3).
In output mode, the values set to each bit are output to the port 3 register (P3). The port 3 function register (PF3)
can be used to specify whether P33 and P34 are normal outputs or N-ch open-drain outputs.
When using this port in input mode, the pin statuses can be read by reading the P3 register. Also, the P3
register (output latch) values can be read by reading the P3 register while in output mode.
A pull-up resistor can be connected in 1-bit units when specified via pull-up resistor option register 3 (PU3).
When using the alternate function as TI4 and TI5 pins, noise elimination is provided by a digital noise eliminator
(same as digital noise eliminator for port 0).
When using the alternate function as A13 to A15 pins, set the pin functions via the memory address output mode
register (MAM). At this time, be sure to set the PM3 registers (PM34, PM35, PM36) and the P3 registers (P34,
P35, P36) to 0.
Clear the P3 and PM3 registers to 0 when using alternate-function pins as outputs. The ORed result of the port
output and the alternate-function pin is output from the pins.
When a reset is input, the settings are initialized to input mode.
(2) Control registers
(a) Port 3 mode register (PM3)
PM3 can be read/written in 8-/1-bit units.
Figure 14-20. Port 3 Mode Register (PM3)
After reset:
FFH
R/W
Address: FFFFF026H
7
6
5
4
3
2
1
0
PM3
PM37
PM36
PM35
PM34
PM33
PM32
PM31
PM30
PM3n
Control of I/O mode (n = 0 to 7)
0
Output mode
1
Input mode
(b) Pull-up resistor option register 3 (PU3)
PU3 can be read/written in 8-/1-bit units.
Figure 14-21. Pull-Up Resistor Option Register 3 (PU3)
After reset:
00H
R/W
Address: FFFFF086H
7
6
5
4
3
2
1
0
PU3
PU37
PU36
PU35
PU34
PU33
PU32
PU31
PU30
PU3n
Control of on-chip pull-up resistor connection (n = 0 to 7)
0
Do not connect
1
Connect
Содержание MPD703030A
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