Could you please explain why the following statement is always FALSE:

IF PLC^.xInitDone AND NOT PLC^.xError THEN

It runs on RaspberryPi with the latest Codesys Runtime.
PLC is a pointer to ModbusSlaveComPort.
The xInitDone is TRUE, xError is FALSE.

If I rewrite the code in such way it works as expected:

IF PLC^.xInitDone THEN
   IF NOT PLC^.xError THEN

What is the result if you replace dereferenced pointers by only boolean variables ?

Hello Sir,

ST checks for all the conditions and does not stop early.

AND_THEN does what you describe with nested ifs.

Best regards,
Marcel

m.prestel hat geschrieben:
Hello Sir,
ST checks for all the conditions and does not stop early.
AND_THEN does what you describe with nested ifs.
Best regards,
Marcel

Sorry Marcel,
I didn't understood your idea.

dFx hat geschrieben:
What is the result if you replace dereferenced pointers by only boolean variables ?

It works as expected.

and if you try :

IF PLC^.xInitDone AND NOT (PLC^.xError) THEN

Sorry I misunderstood you...

Can you provide a small example application to easyly reproduce?

Best regards,
Marcel

dFx hat geschrieben:
and if you try :

IF PLC^.xInitDone AND NOT (PLC^.xError) THEN

Unfortunately it doesn't help. Only nested IFs works fine.
For those who want to reproduce it:

FUNCTION write_value_bool : BOOL
VAR_INPUT
   PLC         : POINTER TO ModbusSlaveComPort;
END_VAR
IF PLC^.xInitDone AND NOT PLC^.xError THEN
        write_value_bool:= TRUE;
ELSE
        write_value_bool:= FALSE;
END_IF

And yes, you have to wait for xInitDone to become FALSE or xError TRUE. For this purpose you can do xReset:= TRUE (at ModbusSlaveComPort) for one cycle.

PhilipLykov hat geschrieben:
… xInitDone to become FALSE or xError TRUE...

This does not match written code. Written code says you have to wait xInitDone to TRUE AND xError to FALSE.

FUNCTION write_value_bool : BOOL
VAR_INPUT
   PLC         : POINTER TO ModbusSlaveComPort;
END_VAR
IF PLC^.xInitDone AND NOT PLC^.xError THEN
        write_value_bool:= TRUE;
ELSE
        write_value_bool:= FALSE;
END_IF

One should avoid the above IF THEN statements. A better solution could be;

write_value_bool := PLC^.xInitDone AND NOT PLC^.xError;

Which (better) readable is something like;

FUNCTION xWrtRdy : BOOL
VAR_INPUT
   pMbCom : POINTER TO ModbusSlaveComPort;
END_VAR
xWrtRdy := pMbCom^.xInitDone AND NOT pMbCom^.xError

Now your code is more atomic in nature and "what's in a name". Also, this function can very easily be transformed to a method of some FB.