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6.2) Connecting Normally Open devices to the Digital Input Lines
When connecting switches, etc, to the Digital Inputs of the PC62C, it is important to
ensure that the inputs are set to a defined state at all times. Figure 6.2 gives an example.
Figure 6.2 gives an example of how to connect a push button to one of the Digital Input
lines on Connector J6. We assume that when the Push button is closed, the Port line will
go high (logic 1 = +5V). When the push button is not closed, the port line should be low.
However, many Users do not connect the ‘pull-down’ resistor to the port line. If this is not
done, the port line will be in a floating state and can hence yield either a high or a low.
Thus you must ensure that the port line is always connected which is done via a resistor
network.
+5V
push button
DIN0
Ground
560R
Rx
Digital Inputs
TTL
Rx = 330R to 1k
INPUTS
Figure 6.2: Connecting Normally Open devices to the Digital Inputs