Emerson Unidrive M700 User Manual page 120

7.2.2 Data structure
Communication between devices is based upon Modbus Application Data Units
(ADUs), the ADU consists of 2 parts, the Modbus Application Protocol (MBAP) header
and the Modbus Protocol Data Unit (PDU).
Figure 7-1 Modbus Data Structure
MBAP Header
Table 7.2 MBAP Header
Field
Transaction Identifier
Protocol Identifier
Length
Unit Identifier
The unit identifier within the MBAP header is used to identify whether the destination
node is the host drive or an option module (not available on the onboard Ethernet
interface with firmware versions prior to V01.02.01.10).
Table 7.3 MBAP Unit Identifier
Unit Identifier
0 or 255
254
120
Modbus ADU
Function Code
Length
(Bytes)
2 Uniquely identifies the transaction (0 to 65535)
2 Identifies the protocol (0 = Modbus)
2 Number of following bytes in the message
1 Uniquely identifies the destination node (0 to 255)
1
2
3
4
Data
Description
Destination
Drive
Slot 1
Slot 2
Slot 3
Slot 4 (onboard Ethernet)
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