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11 OPERATION
Before attempting any serial communication, first ensure that the 8240 Monitors connected to the computer terminal or host
computer by serial link are functioning correctly as individual instruments.
Ensure that the serial data connections to the 8240 Monitor have been made correctly with respect to the computer terminal, or
host computer, interface. If the above check appears satisfactory, test the serial communication by sending an appropriate
message from the computer terminal or host computer to a transmitter and observe if it replies; thus establishing communication.
If communication is not established, check that the computer terminal, or host computer, interface is set up correctly and that the
plug-in links within each transmitter are correctly positioned – see Section 5.
1
2
3
Rx+
Tx+
4
5
6
Rx–
Tx–
Fig. 11.1 Pull-up and Pull-down Resistors (5-wire only)
Computer Terminal or Host Computer
Pull-down
Resistor
Tx–
Tx+
0V
Rx–
Rx+
Pull-down
Resistor
0V
+5V
Pull-up
Resistor
'A'
'B'
+5V
Pull-up
Resistor
'A'
'B'
21
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