● A SEND/RECV instruction cannot be executed for a port where slave communication is in
progress.
● If there is no response, the "master communication sending flags" (YC to YF) remain ON
during the time-out period set in the CPU configuration.
● Up to 16 SEND/RECV instructions can be executed simultaneously for differing COM. ports.
■
Sample program (in the case of CPU with built-in ET-LAN)
● This program sends the MODBUS command (16) from the LAN port of the CPU unit, and
then writes the content of PLC's data registers DT100 to DT101 into the data areas 400001
to 400002 of the external device (MODBUS addresses 0000H to 0001H).
● After it is confirmed that connection 1 is established in master mode (X90) and no
transmissions are currently being executed for the same port (Y90), the SEND instruction is
started.
● The UNITSEL instruction is used to specify a slot number (LAN port: U100) and the
connection number (U1).
● In the SEND instruction, specify and execute PLC's starting address (DT100) and data
amount (U2), MODBUS command (16 = H10), and partner station number (H01) and starting
address (H0). Check addresses of connected devices in the instruction manuals of devices.
R0
R100
UNITSEL U100 U1
SEND.US DT0H1001 H0DT100 U2
R100
SEND
execution
relay
Settings for the communication
port
S1: CPU LAN port (U100)
S2: Connection 1 (U1)
SEND execution conditions
Clear to send flag: ON
Sending flag: OFF
SEND instruction execution
S: Data storage area (DT100)
n: Sent data amount (U2)
D1: MODBUS command (H10)
Partner unit no. (H01)
D2: Destination address (H0)
D3: Execution result code (DT0)
Master
communication
clear to send flag
Master
communication
sending flag
■
Timing chart
Execute SEND
Master communication
sending flag
(Y90 - Y9F)
Master communication
sent flag
(Y70 - Y7F)
Sending data
Response reception
Master communication
clear to send flag
(X90 - X9F)
SEND instruction executable
conditions
Clear to send flag (X90 - X9F): ON
Sending flag (Y90 - Y9F): OFF
Sent flag (Y70 - Y7F):
Normal completion: OFF
Abnormal completion: ON
Sending flag (Y90 - Y9F):
While sending: ON
ED instruction executed following
response reception processing: OFF
Check that the
flag is OFF
Check that
the flag is ON
15.6 SEND (MODBUS Master: Function Code Specification)
15-42 WUME-FP7CPUPGR-12
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