Port 4 - NEC PD789860 User Manual

RD
WR
PORT
WR
PM
PM: Port mode register
RD: Port 2 read signal
WR: Port 2 write signal

6.2.3 Port 4

This is a 4-bit input-only port. Mask ROM versions can specify an on-chip pull-up resistor by means of the mask
option.
The port is also used as key return input.
RESET input sets port 4 to input mode.
Figure 6-4 shows a block diagram of port 4.
Alternate
function
RD
RD: Port 4 read signal
66
CHAPTER 6 PORT FUNCTIONS
Figure 6-3. Block Diagram of P21
Alternate
function
Output latch
(P21)
PM21
Figure 6-4. Block Diagram of P40 to P43
User's Manual U14826EJ5V0UD
P21/TMI
V
DD
Mask option resistor
(mask ROM versions only.
EEPROM versions
have no pull-up resistor.)
P40/KR10 to P43/KR13