Greetings. Very new to Modbus and am using Simply Modbus for this task. In the picture you will see values being written to an MSP430 that represents a serial number. The serial number is:
0202030505

I need to modify the serial number that would include both Alpha and Numeric values. I have no idea as to how this is being encoded. Obviously, 12338 represents 02
12339 represents 03
and so on. However when I try to change the end of the number to represent anything higher than 09, I get an invalid slave ID error. The slave ID is 2.

This is totally over my head lol.
Any suggestions??

 

These are ASCII characters.
https://www.asciitable.com/

Each Modbus (16-bit) register is comprised of two ASCII characters.

It is perhaps easier to understand by looking at the hexadecimal encoding of the value, instead of the decimal encoding. Digits 0 - 9 use hexadecimal codes of 0x30 - 0x39. To express alphabetical characters, the hexadecimal codes 0x41 - 0x5A are used for capital letters.

In your image, if you look in the "bytes" column of each register, you will see the hexadecimal encoding. For the first register (register 521) a value of 3032 is shown. This is two characters - 0x30 and 0x32. If you look these up in the ASCII table linked above, you'll see they equate to characters '0' and '2'.

 

Thank you for that info. I attempted to change the value of 3032 to something else and it would not allow it. However, if I changed 12338 to 12339 it changed the value from 3032 to 3033. It appears I have to change the "Value to Write." However, I can't correlate what that number means to an equivalent ASCII value. Any thoughts?

Thanks for the help!

 

If Simply Modbus does not allow you to enter values as hexadecimal, you will need to convert from hexadecimal to decimal. You can do this with a calculator, such as the following:
https://www.rapidtables.com/convert/number/hex-to-decimal.html

For example, the characters "AB" have a hexadecimal equivalent value of 0x4142 (using the ASCII table I linked previously). Entering this hexadecimal number into the online converter results in a decimal value of 16706.

 

You may find it easier to use a different Modbus software tool that supports viewing and modifying values directly in ASCII or hexadecimal. I believe Modbus Poll allows you to view values as ASCII / Hex:
https://www.modbustools.com/modbus_poll.html