LUXMUX BeST-SLED ISB2, User Manual

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4.2 MODBUS-TCP/IP (Ethernet interface)
MODBUS - TCP/IP is a client/server protocol. The ADU packet structure for each of these
interfaces is shown below. As per the MODBUS Standard, this structure is used
regardless of whether data is being sent from the user or from the device.
MODBUS TCP/IP ADU
MBAP Header MODBUS PDU
Transaction
Identifier
Protocol
Identifier
Length
Unit
Identifier
Function
Code
Data
High Low High Low High Low 1 byte 1 byte 0 up to 252 byte(s)
The MODBUS Application Protocol (MBAP) header is a dedicated TCP/IP header used to
identify the MODBUS TCP/IP ADU. It consists of the Transaction Identifier, Protocol
Identifier, Length, and Unit Identifier (UI). The Transaction Identifier indicates a specific
MODBUS request/response transaction and must be unique at each given time. This
allows the user to associate a particular response with a previous request. The Protocol
Identifier is always 0, which indicates that MODBUS protocol is being used. Length is the
byte count of the Unit Identifier and the MODBUS PDU. The Unit Identifier is a device
identification number (analogous to the Slave Address used in MODBUS-RTU over
Serial). The MODBUS PDU structure is identical for both MODBUS-RTU and MODBUS-
TCP/IP.
4.3 Best-SLED
®
ISB2 Register Map
If users want to develop their own API, Best-SLED® ISB2 Register Map is available upon
request. Please contact technical support:
techsupport@luxmux.com