9.9 Port 8
9.9.1 Overview
Port 8 is a 5-bit input/output port that is also used for CS
3
to CS
0
output,
RFSH
output, and IRQ
3
to IRQ
0
input. Figure 9-8 shows the pin configuration of port 8.
In modes 1 to 6 (expanded modes), port 8 can provide CS
3
to CS
0
output, RFSH output, and IRQ
3
to IRQ
0
input. See table 9-14 for the selection of pin functions in expanded modes.
In mode 7 (single-chip mode), port 8 can provide IRQ
3
to IRQ
0
input. See table 9-15 for the
selection of pin functions in single-chip mode.
The IRQ
3
to IRQ
0
functions are selected by IER settings, regardless of whether the pin is used for
input or output. For details see section 5, Interrupt Controller.
Pins in port 8 can drive one TTL load and a 90-pF capacitive load. They can also drive a
darlington transistor pair.
Pins P8
2
to P8
0
have Schmitt-trigger inputs.
Figure 9-8 Port 8 Pin Configuration
Port 8
P8 /
P8 / /
P8 / /
P8 / /
P8 / /
4
3
2
1
0
0
1
2
3
Port 8 pins
CS
CS
CS
CS
RFSH
3
2
1
IRQ
IRQ
IRQ
IRQ
0
P8 (input)/ (output)
P8 (input)/ (output)/ (input)
P8 (input)/ (output)/ (input)
P8 (input)/ (output)/ (input)
P8 (input/output)/ (output)/ (input)
4
3
2
1
0
Pin functions in modes 1 to 6
(expanded modes)
0
1
2
3
CS
CS
CS
CS
RFSH
3
2
1
IRQ
IRQ
IRQ
IRQ
0
P8 /(input/output)
P8 /(input/output)/ (input)
P8 /(input/output)/ (input)
P8 /(input/output)/ (input)
P8 /(input/output)/ (input)
4
3
2
1
0
Pin functions in mode 7
(single-chip mode)
IRQ
IRQ
IRQ
IRQ
3
2
1
0
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