MODBUS - BigEndian Vs LittleEndian

Ernesto Fantuzzi

1 year ago
updated 1 year ago

Hi,
I've this instrument EASTRON SDM630M

and i'm trying to read it in modbus.
Usually i start my test with modbus pull software.
I'm read the register number 4 - input register FC04 - (Voltage phase 3) in Floating32bit - BIGENDIAN

In comfortclick, to read the same value i need to set LITTLE-ENDIAN.

you can see that in BigEndian the value is incorrect.

Do you know why there is this different from Modbus Poll ?

Thanks in advice.

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Jürgen Jürgenson

1 year ago

Did you try to set -1 on the register too? bOS starts counting from 0. Sometime the manuals show the register addresses as +1.

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Modbus Pull start from zero like bOS.

I think there is an error name in comfortclick because endianess is a standard for reading and it can't be different.

In Big-endian the most significant byte (the “big end”) is stored at the smallest memory address

Address: 0x00 0x01 0x02 0x03
Value: 0x12 0x34 0x56 0x78

In Little-endian the least significant byte (the “little end”) is stored at the smallest memory address

Address: 0x00 0x01 0x02 0x03
Value: 0x78 0x56 0x34 0x12