CHAPTER 6 PORT FUNCTIONS
User’s Manual U14826EJ5V0UD
66
Figure 6-3. Block Diagram of P21
P21/TMI
RD
WR
PORT
WR
PM
Alternate
function
Output latch
(P21)
PM21
Inter
nal b
u
s
Selector
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.
Figure 6-4. Block Diagram of P40 to P43
P40/KR10 to P43/KR13
RD
Alternate
function
V
DD
Mask option resistor
(mask ROM versions only.
EEPROM versions
have no pull-up resistor.)
Internal bus
RD:
Port 4 read signal
Содержание PD789860
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