Modbus

<< Click to Display Table of Contents >>

Navigation:  Hardware Overview > LOG Dataloggers > RMS-LOG-L >

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. To 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.

 

Function 04- Read Input Register

oDevice Data

Register

Parameter

Data type

30001

Serial number

 

Unsigned 32 Bit

30002

30003

Serial number of the probe

 

Unsigned 32 Bit

30004

 

oFloat Values

Register

Parameter

Data type

31001

Value 1

Measurement value 1 of the sensor

Float 32 Bit

31002

31003

Value 2

Measurement value 2 of the sensor

Float 32 Bit

31004

 

oInteger Values

The measurement values are only available in floating format.

 

 

Swap mode

The swap mode defines how a float32 value is represented in MODBUS data structure. The settings must be done with the RMS-CONFIG software.

 

Factory settings: WORD-Swap

 

Example:

Value 1 (Address 31001 / 31002)

45.0 = 0x42340000

Value 2 (Address 31001 / 31002)

1000.0 = 0x447A0000

 

The following website helps for conversion: https://www.h-schmidt.net/FloatConverter/IEEE754de.html

 

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

 

Software Compatibility

The logger is designed for use with the RMS server software (local installation or Rotronic Cloud). The data logger can alternatively also be operated with the RMS-Configuration software (standalone software).

 

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.