Question

When I trace my program (online with breakpoint and singlestep) I see,
that the VAR SOpen becomes “* INVALID: 16#02 *” when the line Step:=Step+1; is reached.

Watching the trace more careful, I saw, that Step changes from 0 to 1, in the first call of “0:”. The two VARs are the two initialized and seem to be linked together. The aditional increase sets Step to 2 (in the 1st run!) and SOpen to invalid.

PROGRAM PLC_PRG
VAR
    SerIO: SERCOMM;
    Step: BYTE := 0;
    Input: ARRAY [0..50] OF DWORD;
    SOpen: BOOL := FALSE;
END_VAR

IF Eingang1 THEN
    CASE Step OF
    0:
        IF NOT SOpen THEN
            SerIO.FB_ACTION := Open;
            SerIO.RECEIVE_BUFFER:=Input[0];
            SerIO.COMPORT:=1;
            SerIO.EN:=TRUE;
            Ausgang1 := NOT SerIO.ERROR;
            SOpen :=TRUE;
            SerIO.EN:=FALSE;
        END_IF;
    1:
        IF SOpen THEN
            SerIO.FB_ACTION:=Read;
            SerIO.EN:=TRUE;
            Ausgang1 := NOT SerIO.ERROR;
            Ausgang2 := (SerIO.BYTES_DONE>3);
            SerIO.EN:=FALSE;
        END_IF;
    2:
        IF SOpen THEN
            SerIO.FB_ACTION:=Close;
            SerIO.EN:=TRUE;
            Ausgang1 := NOT SerIO.ERROR;
            SOpen :=FALSE;
            SerIO.EN:=FALSE;
        END_IF;
    END_CASE
    Step:=Step+1;
    IF Step>2 THEN Step :=0; END_IF;
ELSIF SOpen THEN
    SerIO.FB_ACTION:=Close;
    SerIO.EN:=TRUE;
    SerIO.EN:=FALSE;
    SOpen :=FALSE;
    Step:=0;
END_IF;

Answer 1

I transferred the VAR now to VAR_GLOBAL. That’s not really what I want, but now it works. Better solutions are welcome and will be accepted 🙂