RS Logix structured text

Hi I need some help with RSLOgix 5000 Structured text
I want sound an audible if there is alarm bit but not an acknowedged bit

I have an 2 arrays of 4 DINTS, HMI_ALARM and HMI_ALARM_ACK

RS Logix is complaining about the word/bit referencing such as HMI_ALARM[iWord].iBit


Audible := 0 ;

For iWord := 0 to 4 BY 1 Do

For iBit := 0 to 31 BY 1 Do
If HMI_ALARM[iWord].iBit = 1 AND HMI_ALARM_ACK[iWord].iBit = 0 then
Audible := 1 ;
END_IF ;
End_For ;
End_For ;

To perform indirect addressing in Structured Text, surround all indirect elements with square brackets. Otherwise they are interpreted as though they were named elements of a user-defined tag, not as indirect values.

By itself, HMI_ALARM[iWord].[iBit] can be TRUE or FALSE, but IEC1131 Structured Text doesn't let you compare it to an integer value of 0 or 1 with an "=" operator. You just have to state the BOOL tag by itself, or as the argument of a NOT operator.

Also, limit your DO loop to the values 0, 1, 2, 3 if your array is a DINT[4].

This code should work:

I would just or the 4 words together and check if the result is non zero.

Thanks for the responses. I realised about the 4 after i posted. I need to read up more on Structured text

Peter your reply is a good alternative

I have read that Control Logix I/O runs asynchronously to the PLC scan. I wonder if it will make a difference that you are turning Audible off each time before the checks? If it turns back on it will probably happen so fast that you don't hear it but if Audible drives a relay output there may be issues?

All this is speculation as I have no direct experience with Control Logix and ST.

As usual Peter has his eyes more wide open than most !

As long as the Acknowledge bits are cleared after the Alarm bit is cleared, a simple set of Exclusive OR instructions will work and be much faster.