Modbus¶

Modbus TCP Server¶

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

The device has a Modbus TCP server for direct connection to external devices. The data accessible via Modbus can be found in the table below.

	Details
Protocol	Modbus TCP
TCP Port	502

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

Function 04 – Read Input Register¶

Register	Parameter	Data type
30001	serial number		Unsigned 32 Bit
30002
30003	Probe serial number	Always 0x00000000	Unsigned 32 Bit
30004

Register	Parameter	Data type
31001	Measurement value 1	Temperature value RTD 1	Float 32 Bit
31002
31003	Measurement value 2	Temperature value RTD 2	Float 32 Bit
31004

The temperature values are supplied only as float.

Float Swap Mode¶

Swap Mode is used to set how a Float32 is to be mapped to the Modbus data structure:

45 = 0x42340000 1000 = 0x447A0000

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.)

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.