Group Input negative values ?

lakris

Hello,

 

As I understand, 'Group inputs' are only interpreted as positive integer values.

 

Does anybody know if there is a conversion function so that I can convert to integer with sign.

 

I send values from a Siemens PLC via Profibus/Devicenet gateway and have defined them as an 16 bit Group input.

 

I send them as 16 bit integers with sign [-32768;32767] as twos complement 

 

Do I have to write a conversion function myself or is there a smarter way?

 

Thank You,

lakris

msalminen

I have use following function I made. Remember to select correct notation you need and change it inside my function.

 

I guess you can also try to change your group input to analog input and use it directly. I think you can search this forum to find thread about it.

 

  FUNC num GetSIntGi(
    VAR signalgi giRead)

    ! Function: GetSIntGi 4.9.2006 
    ! Get signed integer from 16bit (bits 0-15) group input.
    ! Bit 15 is the sign bit, so values equal or bigger than 32768 are negatives
    ! and needed to be converted to corresponding negative decimal value
  
    VAR num notation;
    VAR num value;

    ! There are 2 interpretations for negative binary numbers.
    ! Select which notation to use for negative binary numbers.
    ! notation:=1 -- sign magnitude notation - Returned values are between -32767 to 32767
    ! notation:=2 -- two's complement notation - Returned values are between -32768 to 32767
    notation:=2;

    ! Get the integer value from group input (from PLC)
    value:=0;
    value:=GInput(giRead);
 
    ! Convert unsignad integer to the signed integer according the notation used by PLC
    IF notation=1 THEN
      ! Sign magnitude notation
      ! bit15 is sign bit, otherwise same as positive binary numbers
      IF value>32767 THEN
        value:=32768-value;
      ENDIF
    ELSEIF notation=2 THEN
      ! Two's complement notation
      ! bit15 is sign bit, negative values are inverted and added 1
      IF value>32767 THEN
        value:=value-65536;
      ENDIF
    ELSE
      ! Notation not set.
      ! Return value as it is read.
    ENDIF
    RETURN value;
  ENDFUNC

Regards,

Mika

Thilbi

Hi,

you didnA't need a function.
Declare a analog input like this

     -Name "aiShiftingX" -SignalType "AI" -Unit "PB_KARTE" -UnitMap "80-95"
      -MaxPhys 3276.7 -MaxBitVal 32767 -MinPhys -3276.7 -MinBitVal -32767

and you can use the value directly in your program. The range is in this configuration from -3276.7 up to 3276.7.

It is possible to declare an analog input instead a groupinput.

BR
Thilbi

lakris

Thank You very much.

I have defined my inputs as analog inputs instead of group inputs, and it works.