Hardware Overview > LOG Dataloggers > RMS-LOG-L

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	Serial number	Unsigned 32 Bit
30003	Serial number of the probe	Unsigned 32 Bit
30004	Serial number of the probe	Unsigned 32 Bit

oFloat Values

Register	Parameter		Data type
31001	Value 1	Measurement value 1 of the sensor	Float 32 Bit
31002	Value 1	Measurement value 1 of the sensor	Float 32 Bit
31003	Value 2	Measurement value 2 of the sensor	Float 32 Bit
31004	Value 2	Measurement value 2 of the sensor	Float 32 Bit

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.