Hi,

When reading from a coil, what should I put in the "Multibyte Length" which is shown under the "Modbus Data Point Parameters" in my software?
Since I am reading a coil, the associated modbus address (0*4053 in this case) contains only one bit. So, I don't have a multibyte to read from! It is only one bit.

 

The term "Multibyte Length" is not from the Modbus specification, so this must be specific to "your software".

Are you by chance using the Mervis IDE (this was the only thing I could find that uses the terms from your subject)?

According to the guide here:
https://kb.mervis.info/doku.php/en:...ation-protocols-description:3-modbus_settings

It defines the Multibyte Length as follows:

Multibyte length (Parser)
Number of bytes (not registers!) to be read into a data point or to be written into the Modbus table. It is mostly 2, as one Modbus register has 16 bits = 2 bytes. In special applications as e.g. cumulated values in energy meters, which use 4 bytes, the Multibyte Length may be higher. For bit-oriented data points the Multibyte Length = 1 (1 byte is enough - the one which contains the required bit).

So to answer your question, it seems you should use a value of 1 for the Multibyte Length when reading a single coil.

 

The term "Multibyte Length" is not from the Modbus specification, so this must be specific to "your software".

Are you by chance using the Mervis IDE (this was the only thing I could find that uses the terms from your subject)?

According to the guide here:
https://kb.mervis.info/doku.php/en:...ation-protocols-description:3-modbus_settings

It defines the Multibyte Length as follows:

Multibyte length (Parser)
Number of bytes (not registers!) to be read into a data point or to be written into the Modbus table. It is mostly 2, as one Modbus register has 16 bits = 2 bytes. In special applications as e.g. cumulated values in energy meters, which use 4 bytes, the Multibyte Length may be higher. For bit-oriented data points the Multibyte Length = 1 (1 byte is enough - the one which contains the required bit).

So to answer your question, it seems you should use a value of 1 for the Multibyte Length when reading a single coil.

Thanks for the clarification.
Yes, I am using Mervis ID.