9.5.2 Port 4 Registers
Register Configuration: Table 9-7 lists the registers of port 4.
Table 9-7 Port 4 Registers
Name Abbreviation Read/Write Initial Value Address
Port 4 data direction register P4DDR W H'00 H'FF85
Port 4 data register P4DR R/W H'00 H'FF87
1. Port 4 Data Direction Register (P4DDR)—H'FF85
P4DDR is an 8-bit register that selects the direction of each pin in port 4.
Single-Chip Mode: A pin functions as an output pin if the corresponding bit in P4DDR is set
to “1,” and as in input pin if the bit is cleared to “0.”
P4DDR can be written but not read. An attempt to read this register does not cause an error, but
all bits are read as “1,” regardless of their true values.
At a reset and in the hardware standby mode, P4DDR is initialized to H'00, making all eight pins
input pins. P4DDR is not initialized in the software standby mode, so if a P4DDR bit is set to “1”
when the chip enters the software standby mode, the corresponding pin continues to output the
value in the port 4 data register.
Expanded Modes: All bits of P4DDR are fixed at “1” and cannot be modified.
Bit 76543210
P4
7DDR P46DDR P45DDR P44DDR P43DDR P42DDR P41DDR P40DDR
Initial value 00000000
Read/Write WWWWWWWW
155
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