UPD78F9234MC-5A4-A Datasheet, PDF (62/419 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 4 PORT FUNCTIONS
Also, since the option byte is referenced after the reset release, if low level is input to the RESET
pin before the referencing, then the reset state is not released. When it is used as an input port
pin, connect the pull-up resistor.
4.2.4 Port 4
Port 4 is an 8-bit I/O port with an output latch. Each bit of this port can be set to the input or output mode by using
port mode register 4 (PM4). When the P40 to P47 pins are used as an input port, an on-chip pull-up resistor can be
connected in 1-bit units by using pull-up resistor option register 4 (PU4).
The P41 to P44 pins can also be used for external interrupt request input, serial interface data I/O, and timer
output.
Generation of reset signal sets port 4 to the input mode.
Figures 4-8 to 4-11 show the block diagrams of port 4.
WRPU
RD
Figure 4-8. Block Diagram of P40, P45 to P47
PU4
PU40,
PU45 to PU47
VDD
P-ch
WRPORT
WRPM
P4
Output latch
(P40, P45 to P47)
PM4
PM40,
PM45 to PM47
PU4: Pull-up resistor option register 4
P4: Port register 4
PM4: Port mode register 4
RD: Read signal
WR××: Write signal
P40, P45 to P47
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User’s Manual U17446EJ5V0UD