(* Bench test: create PROGRAM PLC_PRG, ST language. Add the SysTime library.
   Add CmpAtomModbus as a library; qualify atMbCall_cext with its namespace if
   the Library Manager requires it. Paste this in the DECLARATION pane. *)
PROGRAM PLC_PRG
VAR
    run : BOOL := FALSE; (* Set TRUE in watch window to start. FALSE closes. *)
    ipAddress : DWORD := 16#C0A80132; (* EDIT: 192.168.1.50 *)
    tcpPort : UINT := 502;
    unitId : BYTE := 1;
    startAddress : UINT := 0; (* Zero-based wire address, not 40001. *)
    registers : ARRAY[0..9] OF WORD;
    status : ARRAY[0..23] OF UDINT;
    handle : UDINT := 0; (* Do NOT retain/persist this. *)
    command : UDINT := 0;
    callResult : UDINT;
    timeResult : UDINT;
    nowUs : SYSTIME;
    nowMs : ULINT;
    lastReadMs : ULINT;
    readDone : BOOL;
    requestError : BOOL;
    hasValidData : BOOL;
    dataStale : BOOL := TRUE;
    lastRequestResult : UDINT;
    lastException : UDINT;
    lastSocketError : UDINT;
    requestErrorCount : UDINT;
    successfulReadCount : UDINT;
    pollDelay : TON;
END_VAR