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4 Using Protocol Macros
4-4
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
In this manual, the protocol structure is explained in simple terms, and examples are given of the
use of the ExecPMCR instruction during control of OMRON devices by using standard system proto-
cols. For details on the protocols, the modification method for standard system protocols, and the
creation method for new sequences, refer to the CX-Protocol Ver.1.9 OPERATION MANUAL (Cat.
No. W344).
Protocols consist of communications sequences. A sequence consists of steps. These steps can be
repeated, or they can be branched or ended depending on the responses received. A step consists of a
command, send/receive messages, processing results, and the next process (which depends on the
processing results).
A protocol consists of processing sequences (such as reading the process value for a Temperature
Controller) for a general-purpose external device. A sequence consists of a group of steps, each of
which consists of a send/receive/control command, send/receive message, processing result, and a
next step that depends on the processing results.
For example, with a sequence that reads the process value for a Temperature Controller, the sequence
sends the send message for the connected Temperature Controller (a character string in which the Pro-
cess Value Read command is inserted between the address and the check code + terminator)
and receives the receive message (a character string in which the Process Value Read command
response is inserted between the address and the check code + terminator).
4-1-3 Protocol Structure
Communications
sequence
Example: Reading the process values
for a Temperature Controller
Transmission of process value reading message and
reception of response message
Step 0
Messages
Step 1
Protocol
NJ-Series
CPU Unit
CJ-Series
Serial
Communications Unit
Command
SEND
(send)
RECV
(receive)
Send message (Example: Process Value Read command)
Header Address Send data Check code Terminator
Receive message (Example: Response)
00 RX00 FCS
RS-232C
or RS-422A/485
Header Address Send data Check code Terminator
00 RX01 FCS
General-
purpose
external device