How to check for non HEX characters in ASCII data

[Aoto10 1]

I have a machine that will sometimes execute the HEX instruction with characters that are not HEX values. The instruction gives the 4100 operation error, the PLC goes to stop and machine will stop entirely. I don't want to change PLC RAS to continue if this error occurs. I have no way of changing the data I receive since it comes from a outside machine. I'd prefer to just check the data before the HEX instruction executes and prevent the execution entirely if the data is going to cause an alarm. I made a sample ladder below of what I came up with to check each of the 4 characters of data. It seems kind of redundant and I feel could be made shorter using different functions. Is there an easier way to do this? If had many more characters this would take many rungs of ladder to accomplish. Thanks.

 

[Gambit 324]

For the test string part you could have used $mov (stringmov).

With LEN you can check the characterlength of the string and than make a FOR NEXT loop checking each character.

Which PLC are you using ? 

 

[Aoto10 1]

1 hour ago, Gambit said:

For the test string part you could have used $mov (stringmov).

With LEN you can check the characterlength of the string and than make a FOR NEXT loop checking each character.

Which PLC are you using ? 

 

Machine has a Q50UDEHCPU. I tried the FOR NEXT loop you mentioned. I see where this accomplishes the same thing with less ladder for a longer string. Is this what you had in mind? I tested and it does work. Could this be improved more? Like using a break to exit the loop if a bad value was found?