NEC mPD789101, User Manual

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CHAPTER 5 PORT FUNCTIONS
User’s Manual U13045EJ2V0UM00
77
5.2.3 Port 2
This is a 6-bit I/O port with output latches. Port 2 can be specified as input or output mode in 1-bit units by using
port mode register 2 (PM2). Use of on-chip pull-up resistors can be specified for pins P20 to P25 in 1-bit units by
using pull-up resistor option register B2 (PUB2).
The port is also used as a serial interface I/O, clock I/O, timer I/O, and external interrupt input.
RESET input sets port 2 to input mode.
Figures 5-4 through 5-7 show block diagrams of port 2.
Caution When using the pins of port 2 as the serial interface, the I/O or output latch must be set according
to the function to be used. For how to set the latches, see Table 13-2 Serial Interface 20 Operating
Mode Settings.
Figure 5-4. Block Diagram of P20
PUB2: Pull-up resistor option register B2
PM: Port mode register
RD: Port 2 read signal
WR: Port 2 write signal
Internal bus
V
DD
P-ch
P20/ASCK20/
SCK20
WR
PUB2
RD
WR
PORT
WR
PM
PUB20
Alternate
function
Output latch
(P20)
PM20
Alternate
function
Selector