Port 4 - NEC 78K0 User Manual

4.2.5

Port 4

Port 4 is an 8-bit I/O port with an output latch. Port 4 can be set to the input mode or output mode in 1-bit units
using port mode register 4 (PM4). Use of an on-chip pull-up resistor can be specified in 1-bit units with pull-up resistor
option register 4 (PU4).
This port can also be used as an address/data bus in external memory expansion mode.
RESET input sets port 4 to input mode.
Figure 4-14 shows a block diagram of port 4.
WR
PU
RD
WR
PORT
WR
PM
PM40 to PM47
Memory expansion
PU4: Pull-up resistor option register 4
PM4: Port mode register 4
RD: Read signal
WR××: Write signal
CHAPTER 4 PORT FUNCTIONS
Figure 4-14. Block Diagram of P40 to P47
PU4
PU40 to PU47
Alternate
function
Selector
Output latch
(P40 to P47)
Selector
Alternate
function
PM4
mode register
(MEM)
User's Manual U15947EJ2V0UD
*
EV
DD
P-ch
P40/AD0 to P47/AD7
111