Structured Text String Alterations

[drbitboy]

Here is an experiment to make my point:

• Create three string tags:
  • four, initialize as '4'
  • ScanSim, initialize as 'P1234'
  • ScanString, initialize as '$00$00$00$00$00$00$00$00'
• Write and run the a program with the following rungs:
  • MOV ScanSim ScanString
    • Simulates barcode read
    • ScanString will be 'P1234' after evaluation of this rung
  • EQU ScanString.DATA[0] 80 DELETE ScanString 1 1 ScanString
    • Strips 'P' prefix
    • ScanString will be '1234' after evaluation of this rung.
    • ScanString.DATA[3] and ScanString.DATA[4] will both be '4' i.e. SINT value 52 decimal = 34H
  • MOV 53 ScanString.DATA[3]
    • Overwrite '4' in string with '5' but leaves stale '4' after string
  • MOV -99 result
    • result is a scalar INT tag
    • Ensure next command's execution can be verified
  • FIND ScanString four 1 result
    • Will overwrite value of -99 from previous rung in result with a value of 0
      • because there will be no one-character sub-string four (='4') in ScanString,
      • which proves the '4' (52 dec = 34Hex) at ScanString.DATA[4] is not part of "STRING" tag ScanString