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Introduction Section 6-1
6-1 Introduction
A message service is a command/response system used for data transmis-
sion between nodes on a network, i.e., PLC to PLC, PLC to computer, and
computer to PLC). The message service can also be used to control opera-
tions, such as mode changes. The message service is implemented by send-
ing commands from the user program. The following communications
instructions are used:
SEND and RECV: Instructions for sending and receiving data.
CMND: An instruction for sending FINS commands. Some FINS commands
are supported by Controller Link Units, and other FINS commands supported
by the PLC’s CPU Unit.
Message service SEND/RECV instructions CMND instruction (FINS commands)
Source
node to
destination
node
PLC to PLC
PLC to
computer
Computer
to PLC
C200HX/HG/HE,
CS/CJ-series, CVM1,
CV-series, or
CQM1H-series PLC
User program
A program is not required for receiving
responses when the PLC executes
SEND and RECV.
SEND
(Com-
mand for
CPU Unit)
C200HX/HG/HE,
CS/CJ-series, CVM1,
CV-series, or
CQM1H-series PLC
(Com-
mand for
CPU Unit)
User program
A program is not required for receiving
responses when the PLC executes
commands.
CMND
(Com-
mand for
Controller
Link Unit)
(Not supported by the
C200HX/HG/HE.)
Command
Command
C200HX/HG/HE,
CS/CJ-series, CVM1,
CV-series, or
CQM1H-series PLC
CS/CJ-series, CVM1,
CV-series, or
CQM1H-series PLC
C200HX/HG/HE,
CS/CJ-series, CVM1,
CV-series, or CQM1H-
series PLC
Computer
A program is required for sending and
receiving data with the computer.
A program is not required for receiving
res
p
onses when the PLC executes commands.
Command
SEND
C200HX/HG/HE,
CS/CJ-series, CVM1, CV-serie
s
or CQM1H-series PLC
(The equivalent of SEND/
RECV and CMND are sent
from the computer pro
gram.)
Computer
Command
(Command for
Controller Link
Unit or CPU
Unit)
Programming is required to receive
responses at the computer.