Comtrol Modbus TCP User Guide - Manual (Page 24)

24 - Chapter 2. Programming Interface DeviceMaster UP Modbus/TCP User Guide: 2000447 Rev. I
Communication Methodology (Receive Raw Data in Slave Mode)
2.2.5.2. Communication Methodology (Receive Raw Data in Slave Mode)
Raw serial and/or EtherNet
device data is returned in
the response to the Read
Holding Registers message
or, optionally, the Read/
Write Multiple Register
message. The data is
requested by accessing the
corresponding receive data
address for the desired port.
The following restrictions
apply to this method:
• The Device Index must be 255 (FF hex) for raw/ASCII serial data and 254 (FE hex) for raw/ASCII
Ethernet device data.
• The variable to receive the data on the PLC must be:
- In the 40xxxx address range. (For Modicon type PLCs.)
- An array of 16 bit words.
- Of sufficient size to contain the sequence number, length, and data field associated with the received
data structure. For more information, see the
2.2.5. Receive Data Message (Raw Data) definition on
Page 23.
• New data will be indicated with an incremented sequence number.
The same data may be returned more than once. However, the same data packet will also return the same
sequence number.
• No data will be indicated with a length of zero.
2.2.5.3. Communication Methodology (Receive Data Master Mode)
Raw serial and/or Ethernet
device data is written to the
PLC at the configured
address.
The following restrictions
apply to this method:
• The Device Index must be
configured for the target
PLC.
• The variable to receive
the data on the PLC
must be:
- In the 40xxxx. (For Modicon type PLCs.)
- An array of 16 bit words.
- Of sufficient size to contain the sequence number, length, and data field associated with the received
data structure.
• New data will be indicated with an incremented sequence number.