What is Byte:Format MB:U8 and LB:U8 in modbus

I have a boiler I can write to registers to change set points in Celcius using Modbus. I am a beginner with this and do not understand the Byte:Format MB:U8 and LB:U8.
Does anyone know where I can find a table with this info. I don't know if its an Integer or REAL or what? I can write a 0 or 255 to this register value
Thanks in advance

Hello,

MODBUS holding/input registers use 2 bytes per register. Is the byte order MSB first or LSB first?

1 byte = 8 bits, 1 register is 2 bytes = 16 bits

Most Significant Byte or Least Significant Byte

For 1 register (2 bytes) you have two choices.

If 2 registers are used, to hold a floating point value, the byte count increases to 4, 2 bytes per register. Now the choice of byte order increases to 4.



The byte must be correct for proper communication of the value.

> MB:U8 and LB:U8

That indicates to me MSB first unsigned or LSB first unsigned. Unsigned meaning a byte value 0 - 255. Since it is only one byte the S was dropped.

So, the byte is placed in the first 8 bits of the 16 bit register or the second 8 bits of the 16 bit register. The value is not a float. It is an unsigned small integer.

One other thing, the bit order might be swapped. From the text you posted "MB:U8 and LB:U8" I am "guessing" it is the byte position in the register.

FYI, integer means different things in/on different computer languages/computers. If you do not know, check the documentation.

http://accautomation.ca/what-everybody-ought-to-know-about-plc-programmable-logic-controller-numbering-systems/

The above is a reference to numbering systems in PLCs.

Regards,
Garry
http://www.accautomation.ca