Functions; Read Holding Registers Command (0X03) - Siemens SINAMICS PERFECT HARMONY GH180 Function Manual

Modbus Ethernet Communication

4.5 Functions

4.5 Functions
Supported Command Set
The NXGpro Control implements the following Modbus™ commands:
● Read holding registers (function code 0x03)
● Write single register (function code 0x06)
● Write multiple registers (function code 0x10)
Commands are issued by the Modbus™ master (PLC) and sent over the network to the
Siemens slave[s]. The request and response message prefix for all codes is a 6 byte prefix,
as defined in the following table.
Transaction identifier
Transaction identifier
Protocol identifier
Protocol identifier
Length field (upper byte)
Length field (lower byte)
Commands are listed and described in the sections that follow.
4.5.1

Read Holding Registers Command (0x03)

Description
The "read holding registers" command allows the Modbus master to read up to 64 consecutive
memory registers from the drive.
Example
A sample of a "read holding registers" request to read 2 registers (40005 and 40006) and the
associated response, in hexadecimal, is given below.
Read Holding Registers Command
TX (Request)
RX (Response)
The meaning of the sample request and associated response is detailed in the following tables.
102
Definition of Byte
usually 0 (copied by server)
usually 0 (copied by server)
0
0
0 (all messages are less than 256 bytes)
number of bytes to follow
01 03 00 04 00 02 -- --
01 03 04 04 A5 90 B1 -- --
Number
NXGpro Communication
Function Manual, AB, A5E33486415A