Modbus

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Modbus

MODBUS communication protocol

 

Important:

Please read out the MODBUS byte order of the RMS device with RMS-CONFIG prior to any programming.

 

For direct connection to other systems, the device provides a MODBUS TCP server. Following data is available via MODBUS communication:

Description

Details

Protocol

MODBUS TCP

TCP Port

502

 

When reading out data from the input register select the index=-1.

 

MODBUS register

Device data (FC4: Read Input Registers)

Address

Number

Parameter

Data type

Comment

30000

2

Serial number

Unsigned 32 Bit

SN in Hex: e.g. 01ACCBE1 = 28101601

 

Output (FC1: Read Coils)

Address

Number

Parameter

Data type

Comment

0000

16

Status of digital outputs

Unsigned 16 Bit

Bit 0 = status of output 1

Bit 1 = status of output 2

 

(FC5: Write Single Coil)

Address

Number

Function

Data type

Comment

0000

0001

1

Relays: set

Relays: reset

Unsigned 16 Bit

FF00: set relay

0000: reset relay

 

The RMS LAN devices (except the RMS-Converter) are based on a Little Endian memory organisation (The device firmware provides the MODBUS information starting with the most significant byte.)

 

NoChange (Little Endian)

Word Swap (Middle Endian)

31001

0

0x0000

31001

13378

0x3442

31002

13378

0x3442

31002

0

0x0000

31003

0

0x0000

31003

31300

0x7A44

31004

31300

0x7A44

31004

0

0x0000

Byte Swap (Mixed Endian)

Byte and Word Swap (Big Endian)

31001

0

0x0000

31001

16948

0x4234

31002

16948

0x4234

31002

0

0x0000

31003

0

0x0000

31003

17530

0x447A

31004

17530

0x447A

31004

0

0x0000

 

Connection timeout: When TCP connection is open and for more than 30 seconds no communication is performed, the device automatically closes the TCP connection. In case of a communication interruption, this prevents the socket being blocked.

 

Additional MODBUS details can be found here: MODBUS in RMS.

 

Updated: 13.12.2023.