Modbus‑TCP Communication Protocol
‑17‑
Field Length
Description
Client
Server
Length 2 bytes Number of
following bytes
Initialized by the
client (Request)
Initialized by the
server
(Response)
Unit identifier 1 byte Identification of
a remote slave
connected on
the serial line or
on other buses
Initialized by the
client
The server
copies the value
from the
received request
In theory, the host controller can read a maximum of 12 consecutive parameters.
However, the last parameter it reads cannot jump to the next parameter group.
Otherwise, a response error occurs.
The slave read response error command is 0x83. The write response error command
is 0x86. The multi‑write response error command is 0x90.
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