CHAPTER 4 PORT FUNCTIONS
Preliminary User’s Manual U19014EJ1V0UD
70
4.2.3 Port 3
Port 3 is a 4-bit I/O port with an output latch. Port 3 can be set to the input mode or output mode in 1-bit units
using port mode register 3 (PM3). When the P30 to P33 pins are used as an input port, use of an on-chip pull-up
resistor can be specified in 1-bit units by pull-up resistor option register 3 (PU3).
This port can also be used for external interrupt request input and timer I/O.
Reset signal generation sets port 3 to input mode.
Figures 4-10 and 4-11 show block diagrams of port 3.
Cautions 1. Be sure to pull the P31 pin down before a reset release to prevent malfunction.
2. When writing the flash memory with a flash memory programmer, connect P31/INTP2/OCD1A
as follows.
•
P31/INTP2/OCD1A: Connect to EV
SS
via a resistor (10 k
Ω
: recommended).
The above connection is not necessary when writing the flash memory by means of self
programming.
Remark
The P31 and P32 pins of the
µ
PD78F0730 can be used as on-chip debug mode setting pins (OCD1A,
OCD1B) when the on-chip debug function is used. For details, see
CHAPTER 20 ON-CHIP DEBUG
FUNCTION.
Figure 4-10. Block Diagram of P30 to P32
P30/INTP1,
P31/INTP2/OCD1A,
P32/INTP3/OCD1B
WR
PU
RD
WR
PORT
WR
PM
PU30 to PU32
Alternate
function
Output latch
(P30 to P32)
PM30 to PM32
EV
DD
P-ch
Selector
Internal bus
PU3
PM3
P3
P3:
Port register 3
PU3:
Pull-up resistor option register 3
PM3:
Port mode register 3
RD: Read
signal
WR
××
: Write
signal
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