5.5 Port 4
Port 4 is an 8-bit input/output port that also provides pins for interrupt input (IRQ
0
to IRQ
2
), A/D
trigger input, system clock (Ø) output, and bus control signals (in the expanded modes).
Pins P4
7
to P4
3
have different functions in different modes. Pins P4
2
to P4
0
have the same
functions in all modes. Table 5-11 lists the pin functions.
Table 5-11. Port 4 Pin Functions
Pin
Expanded modes
Single-chip mode
P4
0
P4
0
input/output , IRQ
2
input, and ADTRG input (simultaneously)
P4
1
P4
1
input/output and IRQ
1
input (simultaneously)
P4
2
P4
2
input/output and IRQ
0
input (simultaneously)
P4
3
RD output
P4
3
input/output
P4
4
WR output
P4
4
input/output
P4
5
AS output
P4
5
input/output
P4
6
Ø output
P4
6
input or Ø output
P4
7
WAIT input
P4
7
input/output
Pins of port 4 can drive a single TTL load and a 90pF capacitive load when they are used as output
pins.
Table 5-12 details the port 4 registers.
Table 5-12. Port 4 Registers
Name
Abbreviation
Read/Write
Initial value
Address
Port 4 data direction register
P4DDR
W
H'40 (modes 1 and 2)
H'FFB5
H'00 (mode 3)
Port 4 data register
P4DR
R/W
*1
Undetermined
*2
H'FFB7
Notes: *1 Bit 6 is read-only.
*2 Bit 6 is undetermined. Other bits are initially “0.”
88
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