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Overview of the Protocol Macro Functions Section 5-1
OMRON devices using standard system protocols. For details on the proto-
cols, the method of modifying the standard system protocols, and the method
of creating new sequences, refer to the CX-Protocol Operation Manual
(W344).
5-1-3 Protocol Structure
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 Temper-
ature Controller (a character string in which the Process Value Read com-
mand is inserted between the header + 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 header +
address and the check code + terminator).
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
Serial
Communications Unit
(CS/CJ Series)
SEND
(send)
RECV
(receive)
RS-232C or
RS-422A/485
General-purpose external device
Send message (Example: PROCESS VALUE READ command)
Header Address Send data Check
code
Terminator
Receive message (Example: Response)
CPU Unit
Serial Communications Board
(CS Series only)
RX00
RX01
Header Address Send data Check
code
Terminator
Command
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