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10
DEDICATED INSTRUCTIONS
Function
10 - 6
(1)
MODBUS device data are read from and written to the slave specified in the
target IP address of the control data.
(2)
The processing used in the automatic communication function can be performed
from a sequence program at any timing.
(3)
A maximum of eight MBRW instructions can be executed simultaneously.
Any instructions attempted in excess of the limit are ignored.
Create a sequence program carefully so that the number of simultaneously
executed MBRW instructions does not exceed 8.
(4)
The QJ71MT91 automatically opens a TCP connection with a target slave when
this instruction is executed.
(5)
Whether TCP connection closing processing is performed or not can be selected
in "Execution type ((S1)+0)" of the control data.
When communication with the same target device is made frequently using the
dedicated instruction, setting "TCP connection is not closed after instruction
completion" saves the time required for TCP connection opening for the
subsequent instruction execution.
(6)
Whether the MBRW instruction is being executed or not and whether it is
completed normally or not can be confirmed in the MODBUS exception code
((S1)+2), and the completion device (D2) and completion status indication flag
((D2)+1) specified in the set data.
(a)
MODBUS exception code
Stores the exception code when the processing in the slave is completed
with an error.
(b)
Completion device (D2)
Turns ON in the END processing of the scan where the MBRW instruction
is completed, and turns OFF in the next END processing.
(c)
Completion status indication device ((D2)+1)
Turns ON/OFF depending on the status of the MBRW instruction
completion.
Normal completion:
Error completion :
Remains OFF.
Turns ON in the END processing of the scan where
the MBRW instruction is completed, and turns OFF
in the next END processing.
MELSEC-Q
10 - 6
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