LG GLOFA-GM Series User Manual page 218

Chapter 7 Communication function
In program of [Figure 7.17], RD_START is a contact point to start READ F/B and is set after WRITE
F/B is executed. An initial value of it is set to operate READ F/B at the first scan of program.
WR_START is a contact point to start WRITE F/B and is set after READ F/B is executed to run WRITE
FB. All two variables are allocated to auto-variables. After one dedicated Function Block is executed
through the contact point and 1 sec. timer above, operation in order by the next Function Block is
available in a cycle of I sec. 1 sec. timer is used to prevent unnecessary communication overload by
setting the min. execution cycle of Function Block to 1 second. This timer is adjustable based on
application conditions of user's.
If program of [Figure 7.17] is downloaded to PLC set to master station, programming for 3 stations
communication in [Figure 7.16] is completed. No need to prepare communication program or to set
frame in slave PLC. Communication will be started if PLC program is switched to operation Run by
setting Cnet I/F module to dedicated mode as connected with RS-422 cable. If communication is
normal, NDR output of 'GM_RD' & 'GM_WR' Function Blocks is turned ON in accordance with the
execution cycle of Function Block, and if communication is not normal, ERR output is ON with error
code displayed on STATUS. [Table 7.25] describes error status according to output STATUS values in
case error occurs. Refer to those actions to take to check for the cause of errors.
[Table 7.25] Error codes and Actions to take when dedicated F/B is executed
STATUS
value(dec.)
10 No response from correspondent station.
Position of Cnet I/F module is incorrectly
17
specified.
21 No response from Cnet I/F module
NAK from correspondent station has been
35
received.
37 Input parameter setting is incorrect
Meaning
7-99
Action to take
1) Check setting of correspondent station No.
2) Check dedicated mode for operation of
correspondent station.
3) Check communication basic parameters
1) Check if SLOT_NO value is correct.
1) Check operation mode of local Cnet I/F module
2) Check channel No.
1) Check variable name (%MB,%QB,%IB – BYTE
only available)
2) Check data length