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7.8 Port 8
7.8.1 Overview
Port 8 is a 4-bit input/output port that is also used for IRQ
pin configuration of port 8.
Pin P8
input pins or IRQ
pins in modes 2 and 3.
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
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functions as input/output pin or as an IRQ
0
to IRQ
input pins in mode 1, and as input/output pins or IRQ
3
1
to P8
have Schmitt-trigger inputs.
2
0
Port 8 pins
P8
/IRQ
3
3
P8
/IRQ
Port 8
2
2
P8
/IRQ
1
1
P8
/IRQ
0
0
Figure 7-17 Port 8 Pin Configuration
to IRQ
3
0
input pin. Pins P8
0
Mode 1
P8
(input)/IRQ
(input)
3
3
P8
(input)/IRQ
(input)
2
2
P8
(input)/IRQ
(input)
1
1
P8
(input/output)/IRQ
(input)
0
0
146
input. Figure 7-17 shows the
to P8
function as either
3
1
to IRQ
input
3
1
Modes 2 and 3
P8
(input/output)/IRQ
(input)
3
3
P8
(input/output)/IRQ
(input)
2
2
P8
(input/output)/IRQ
(input)
1
1
P8
(input/output)/IRQ
(input)
0
0
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