LG GLOFA-GM Series User Manual page 318

Chapter 9 Diagnosis function
Chapter 9 Diagnosis function
9.1 Loop-Back self diagnosis
Loop-Back self diagnosis is a checking function if this module operates normally by itself as not connected with external
devices via communication cable. Through this function, self-diagnosis is available for all hardware of Cnet I/F module
except for external communication line and RS-232C/RS-422 channels also can be tested simultaneously. For Loop-
Back self diagnosis, set operation mode switch of the module to test mode.
Remark
[Note1] GM7(G7L-CUEB/G7L-CUEC) series isn't provided with the diagnosis function.
9.1.1 Principle of operation
Loop-Back test sends test data from computer link itself without external cable connection to RS-232C/RS-422
channels and receives the data to display the diagnosis result on LED as compared with the sent data. [Figure 9.1]
shows data flow in Loop-Back mode.
[Figure 9.1] Data flow chart in Loop-Back mode
PLC CPU
PLC CPU
RS-232C Channel
RS-232C Channel
TX
TX
RX
RX
RS-422 Channel
RS-422 Channel
TX
TX
RX
RX
RS-232C Cable
RS-232C Cable
RS-422 Cable
RS-422 Cable
9-1