Digi One IAP and PLC2 Unprotected Read Messaging

[Ian762]

Hello,


I am using a Digi One IAP and CompactLogix PLC to read some Modbus registers from a Kohler Generator. Things are working, except when I want to read some of the higher numbered registers, i.e. anything over 24599. In order to get to the full range of registers, I need to use PLC2 Unprotected Reads, however the documentation from the Digi One website does not show an example of how to do so. It just says to put in the address direct, but this is not accepted by Studio 5k as a valid Source Element.


Anyone have experience with this?

-Thanks


(I saw someone posted this a few years ago, however there was no solution.)

 

[Ian762]

Digi One manual text:


1.7 Reading Modbus 4x values


The SLC Typed Readto N-file types map to a read of Modbus 4x holding registers. Below are the algorithms for mapping:


•For files N0-N10, use the starting element as the Modbus address. For example, N7:0 and N10:0 map to Modbus 4x00001, while N10:17 maps to Modbus 4x00018. Files N0 to N9 are treated like N10.

•For files N11 to N255, subtract 10 from the file number, multiply this number by 100 and add the starting element. For example, N21:0 is Modbus 4x01101 since ((21 – 10) * 100) + (0 + 1) is 1101. Register N170:17 is Modbus 4x16018 since ((170 – 10) * 100) + (17 + 1) is 16018. The maximum address is thus N255:255 for 4x24757. This may appear complex, but a simple Excel spreadsheet can clearly document your mappings.



If you need access to all 65,535 Modbus registers, use the PLC2 or CIF Unprotected Read. These reads map directly into Modbus registers. A CIF read of offset 0 maps to Modbus 4x00001, offset 100 maps to Modbus 4x00101, and so on. This off-by-one behavior occurs because Modbus register 4x00001 is actually sent on the wire as address 0, not 1.