UPD784938 Datasheet, PDF (155/733 Pages) NEC – 16-Bit Single-Chip Microcontrollers

CHAPTER 6 PORT FUNCTIONS
6.6 Port 4
Port 4 is an 8-bit input/output port with an output latch. Input/output can be specified in 1-bit units by setting the port 4 mode
register (PM4). Each pin incorporates a software programmable pull-up resistor. This port has direct LED drive capability.
Port 4 also functions as the time division address/data bus (AD0 to AD7) by the memory expansion mode register (MM) when
external memory or I/Os are expanded.
When RESET is input, port 4 is set as an input port (output high-impedance state), and the output latch contents are undefined.
6.6.1 Hardware configuration
The port 4 hardware configuration is shown in Figure 6-37.
Figure 6-37. Port 4 Block Diagram
WRPUOL
Pull-up resistor option register L
PUOL4
RDPUOL
VDD
MM0 to MM3
WRPM4
Port 4 mode register
RDPM4
PM4n
Internal
data
bus
WRP4
RDP4
Output latch
P4n
P4n
n = 0 to 7
Input/
output
control
circuit
Internal
address
bus
Preliminary User’s Manual U13987EJ1V0UM00
155