Application Data Unit (Adu) - Fronius Ri Fb Inside/I Bedienungsanleitung

Application Data
This section describes the encapsulation method used for a MODBUS request or
Unit (ADU)
response when it is transmitted over a MODBUS TCP network.
Description of MPAP header:
Transaction Identifier
Used to allocate the transaction. The MODBUS server copies the Transaction
Identifier of the request into the response.
Transaction Identifier
This is used for transaction pairing. The MODBUS server copies the transaction
identifier from the request into the response.
Length:
Description:
Client:
Server:
Protocol Identifier
This is used for multiplexing within the system. The MODBUS protocol is iden-
tified by the value 0.
Length:
Description:
Client:
Server:
Length
This field is used to specify the number of bytes in the field to follow, including
the unit identifier, function code, and data field.
Length:
Description:
Client:
Server:
Unit Identifier
This field is used for routing within the system. It is usually used for communi-
cation with a serially connected MODBUS- or MODBUS+ slave where commu-
nication takes place via a gateway between an Ethernet network and a serial
MODBUS line. The field value is set in the request by the MODBUS client and
must be replicated exactly in the response from the server.
Length:
Description:
Client:
All MODBUS/TCP ADUs are sent via TCP on registered port 502.
MPAP header
2 bytes
For identifying a MODBUS request/response transac-
tion
Initialized by the client
Copied back by the server from the request received
2 bytes
0 = Modbus protocol
Initialized by the client
Copied back by the server from the request received
2 bytes
Number of bytes to follow
Initialized by the client
-
1 byte
For identifying a remote slave that is connected via a
serial line or other type of bus.
Initialized by the client
Englisch (US)
Function code Data
67