AccuEnergy Acuvim II series

159
Modbus Client Modbus Server
Request Indication
Confirmation Response
Fig 5-41
1. Protocol
a. Data Frame Format
Table 5-2
MBAP Header Function Data
7x8-Bits 8-Bits Nx8-Bits
b. Modbus Application Header (MBAP Header) Field
The Modbus application header eld is the start of the data frame and consists
of seven bytes.
Table 5-3
Field Length Description
Transaction
Identier
2 Bytes Identication of a Modbus Request/Response transaction
Protocol Identier 2 Bytes Modbus protocol=0
Length 2 Bytes Number of following bytes
Unit Identier 1 Byte Slave address, in the range of 0~247 decimal.
c. Function Field
The function code eld of a message frame contains eight bits. Valid codes are
in the range of 1~255 decimal. When a message is sent from a client to a server
device the function code eld tells the server what kind of action to perform.