Considerations For Data Communication - Mitsubishi Electric MELSEC iQ-R Series User Manual

3.3

Considerations for Data Communication

The following describes considerations for data communications using the nonprocedural protocol.
Factors that initialize the C24 transmission sequence
The initial status means the status where transmission has stopped and received data has been discarded.
C24 transmission sequence initialization factors are as follows.
• When the power is turned ON, the CPU module is reset, or the C24 mode is switched.
• When the received data was cleared.
• When the CD (DCD) signal turns OFF when data is communicated with the full-duplex communications on the RS-232 side
with the CD terminal check enabled.
Generation of framing error on target device
When nothing is transmitted from C24 to a target device through the RS-422/485 interface, a framing error may be generated
by the noise etc, on the target device side.
Send an arbitrary code first so that the target device identifies the head of the data transmitted from C24.
Check the C24 interface specifications before data communication.
Data communications with target device using the multidrop connection
When communicating data by the multidrop connection between the target device and the CPU module in a 1:n basis, data
transmitted by the target device is received by C24.
For the multidrop connection, data reception using a user frame should be performed. (Page 278 Data Reception)
If data is not received by user frame, create a program that ignores (reads and discards) the received data other than the
received data addressed to the host station, including the data indicating the target CPU module in the message.
Ex.
STX Space Station
No. 0
( ) ( ) ( )
02 20 30
H H H
Retry processing for data reception errors
The data when reception error occurred is discarded and only the data for the normal reception is taken into the C24.
For this reason, the received message may be missing data if reception error occurs.
To assure the correct transmission and reception of data, it is recommended that a normal/error response message is
received and a response message reception timeout check is conducted for the data transmitted between the CPU module
and the target device, and that measures such as retransmitting the data (transmission retry) is taken when an abnormal
response is received or when an error timeout occurs.
Station Data length
No. 2
(BIN data)
( )
32
H
3 DATA COMMUNICATION USING NONPROCEDURAL PROTOCOL
Data CR LF
( ) )
0D (0A
H H
3.3 Considerations for Data Communication
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