Map each Modbus-read sensor ID to its factory serial number and assign a default string before evaluating the lookup. The default remains active whenever the input ID has no matching entry.
Define the lookup behavior
The function block input is a DWORD, while the factory serial number is a STRING. The confirmed mappings are:
| Input sensor ID | Factory serial number |
|---|---|
| 10091474 | 52580 |
| 10091464 | 52585 |
| 10090645 | 52597 |
| 10089558 | 52599 |
| 10089559 | 52604 |
Assign the default before the IF statements
Write the unknown-ID result at the start of every execution, then overwrite it only when a comparison succeeds. This prevents the output from retaining a serial number produced during an earlier execution.
FactorySerial := 'Not in list';
IF Input = 10091474 THEN
FactorySerial := '52580';
END_IF;
IF Input = 10091464 THEN
FactorySerial := '52585';
END_IF;
IF Input = 10090645 THEN
FactorySerial := '52597';
END_IF;
IF Input = 10089558 THEN
FactorySerial := '52599';
END_IF;
IF Input = 10089559 THEN
FactorySerial := '52604';
END_IF;This is the smallest correction to the existing logic. If none of the comparisons evaluates true, FactorySerial remains 'Not in list'.
Scale the mapping with a constant structure array
For approximately 150 mappings, the evidence also supports storing input and serial values together in a constant array, scanning it with a FOR loop, and leaving the loop with EXIT after a match. The demonstrated declaration syntax applies to CoDeSys 2.3; confirm that the target ST environment supports constant arrays of structures before adopting it.
- Define a structure containing an input value and its corresponding serial string.
- Declare the mapping array and a constant representing its element count.
- Set the output to
'Not in list'before starting the loop. - Compare each array entry with the input, copy the matching serial number, and execute
EXIT. - When adding mappings, update both the array contents and its declared element count.
Verify known and unknown IDs
Test at least one known value, such as 10091474, and confirm that the output becomes '52580'. Then apply an ID absent from the table and confirm that the output becomes 'Not in list'. Finally, change from a known ID to an unknown ID during consecutive executions; the output must change to the default instead of retaining the previous serial number.
FAQ
How do I return “Not in list” for an unknown ID in Structured Text?
Assign FactorySerial := 'Not in list'; before the lookup statements. A matching comparison then overwrites that default.
Why does the serial-number output retain the previous sensor value?
The output was not reset before the lookup. Assign the default during every execution so an unmatched ID cannot leave the earlier result in place.
How should I maintain 150 sensor ID mappings in ST?
If the target environment supports it, place the ID and serial pairs in a constant array of structures and search it with a FOR loop. Use EXIT immediately after finding a match.
