8 Loopback Test
8-2
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
8-1
Executing Loopback Tests
The loopback test is a testing function for a communications circuit. The Serial Communications Unit
compares transmitted data and loopback data. To perform loopback tests, connect a loop backwire con-
nector to the port of Serial Communications Unit.
Make the connections according to the type of port, as shown in the following diagrams.
z
RS-232C Port
z
RS-422A/485 Port
The loopback test is performed using the procedure shown below.
1
Connect the connector of the port to be used to execute the loopback test. See 8-1-2 Connec-
tion Method for details.
2
Set the serial communications mode to Loopback Test (F hex) using the applicable CJ-series
Unit Device Variables for System Setting. Refer to 8-2-1 Device Variables for CJ-Series Unit for
System Settings.
3
Set the following communication settings for the loopback test in the Device Variables for CJ-
Series Unit for System Settings: Baud Rate, Stop Bits, Parity, and Data Length. For details, refer
to 8-2-1 Device Variables for CJ-Series Unit for System Settings.
8-1-1
Overview
8-1-2
Connection Method
8-1-3
Procedure
Loopback test
Loopback test switch
The loopback test results
are stored.
Serial Communications Unit
Pin
Signal
2
3
4
5
1
8
7
SD
RD
RTS
CTS
FG
DTR
DSR
Pin
Signal
1
2
3
4
RDA
RDB
SDA
SDB