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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 bitwise. I/O settings are controlled via the port 3
mode register (PM3).
During output mode, the values set to each bit are output to the port register (P3).
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 resistance can be connected bitwise when specified via the pull-up resistance option register 3 (PU3).
When using the alternate function as TI4 and TI5 pins, noise elimination is provided by a digital noise elimination
circuit (same as digital noise elimination circuit 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). The PM3 register (PM34 to PM36) must be set to 0.
Clear (to "0") the P3 register and the PM3 register 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)
Read and write in 8-bit units and bitwise are enabled.
FFH
After reset:
7
PM3
PM37
PM3n
0
1
340
CHAPTER 14
Figure 14-15. Format of Port 3 Mode Register (PM3)
R/W
Address: FFFFF026H
6
5
PM36
PM35
Output mode
Input mode
PORT FUNCTION
4
3
PM34
PM33
PM32
Control of I/O Mode
2
1
0
PM31
PM30
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