micrologix null value?

[ryrzu]

Hello,
Is it possible to put null or delete value in data table in micrologix?
Micrologix is using modbus to get data and store it in integer (N) data file. Then data is read by rslinx. If modbus communication fail data in file remain unchanged so in rslinx (and further in my application) i get old data which i simply don't want to have because its hard to spot when there was communication lose and when data was simply static. I prefere to have empty fields - it will not populate my database with false data and allow to notice communication error faster.

 

[Jeff23spl]

why not just clearing all the value when you have a communication error bit set to 1 or something like that ?

 

[Ken Roach]

Is zero ever a valid data value for your process ?

If not, you can just use the .ER bit of the Modbus message instruction to populate the target data fields with zeroes. Use the MOV or FLL instructions.

 

[ryrzu]

Thank you for replies.
Unfortunately "0" can be valid. Moreover those are readings from meters (WAGES) and no data is better than bad data in further reports.

 

[daba]

You could fill the data fields with "nonsense" data, -32768, for instance. Or, you could read the "data is valid" flag, and simply NOT read the data if it isn't valid.

The thing about Logix5/Logix500 data-tables, and Logix5000 tag databases, is that none of them have the functionality of a "proper" database, where a data-location can be "empty" or "uninitialised". They all have to contain valid data for the data-type, since every bit is used.