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CHAPTER 4 PORT FUNCTIONS
Preliminary User’s Manual U16035EJ1V0UM
4.2.4 Port 3
Port 3 is a 3-bit I/O port with output latch. P34 to P36 pins can specify the input mode/output mode in 1-bit units
with port mode register 3 (PM3). Use of an on-chip pull-up resistor can be specified for the P34 to P36 pins in 1-
bit units by pull-up resistor option register 3 (PU3).
Port 3 can also be used for serial interface data I/O and clock I/O.
RESET input sets port 3 to input mode.
Figures 4-6 and 4-7 show block diagrams of port 3.
Cautions 1. When reading port 3 using an 8-bit memory manipulation instruction, do not use the lower
4 bits (P33 to P30) because they are undefined. When writing port 3 using an 8-bit memory
manipulation instruction, any values can be written to the lower 4 bits. Execution of a 1-bit
memory manipulation instruction for the lower 4 bits is prohibited.
2. Be sure to set the lower 4 bits (PM33 to PM30) of port mode register 3 (PM3) to 1.
Figure 4-6. Block Diagram of P34 and P36
Internal bus
V
DD0
P-ch
P34/SI31,
P36/SCK31
WR
PU
RD
WR
PORT
WR
PM
PU34, PU36
Alternate
function
Output latch
(P34, P36)
PM34, PM36
Selector
PU:
Pull-up resistor option register
PM: Port mode register
RD: Port 3 read signal
WR: Port 3 write signal