Datasheet

CHAPTER 4 PORT FUNCTIONS
User’s Manual U18172EJ3V0UD
66
4.2.3 Port 4
Port 4 is a 2-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)
Note
. When the P40 and P43 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).
Reset signal generation sets port 4 to the input mode.
Figures 4-11 shows the block diagram of port 4.
Note In
μ PD78F920x, set PM41, PM42, and PM44 to PM47 to "0" at program initialization.
Figure 4-11. Block Diagram of P40 and P43
P40, P43
WR
PU
RD
WR
PORT
WR PM
PU40, PU43
PM40, PM43
V DD
P-ch
PU4
PM4
Internal bus
Output latch
(P40, P43)
Selector
P4
P4: Port register 4
PU4: Pull-up resistor option register 4
PM4: Port mode register 4
RD: Read signal
WR××: Write signal
4.3 Registers Controlling Port Functions
The ports are controlled by the following four types of registers.
• Port mode registers (PM2 to PM4)
• Port registers (P2 to P4)
• Port mode control register 2 (PMC2) (
μ PD78F920x only)
• Pull-up resistor option registers (PU2 to PU4)
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