Hello All

Under PCS7 --> WinCC, refer the below C Script for "Text Display". This code is extracted from PIDConS faceplate for text display by name "Manual". We have to connected status1 tag for the property. Need some help in understanding the statement "#define BIT (i, status)" and how the script gets the value of bit status at position 3.  Pasting the script below

Nil

Hello,

Further to my above post, what I dont understand is the need for "i" to "shift left" by 1.

We know the status of each bit in the DWORD tag "Status1" and can be directly "&" to get the value. Need some feedback please.

Regards

I assume you mean this part:

 (((unsigned long)status & (1 << i))!=0)

That is not shifting to the left by 1.  It's shifting to the left by the called parameter 'i' and comparing it to 0.  

so its just basically a case statement, based on when each bit & operation is != 0.  where only 1 IF can be true because of the construction of the Status1 by the design of the block for this purpose

if(  BIT(3,value) ) // Bit3= Out of service
{...
}

 evaluates the {...} section only when bit 3 passes the test in that case.  Same for each other If/else test.

So it's doing exactly what you said, its evaluating each bit directly.

 Refer above code.

Based on PID Block Status1 bit information, Out of Service= Bit 3 position & Automode enable=Bit 5 postion. In fact the arguments passed from if and elseif have the exact bit information to be processed. What is the need for shifting the bit position left by "1" (refer #define statement). Hope you got my question.

Regards

As I already said, It is not "shifting left by 1".  It is shifting '1' left by the index ' i ' value # of positions.  This is a standard bitwise function in many programming languages.

Like this table.

1<<0 = `00000001`
1<<1 = `00000010`
1<<2 = `00000100`
1<<3 = `00001000`
1<<4 = `00010000`
1<<5 = `00100000`

That means that in this case, their values will look like this in binary and then this value is & with the Status1 for the logical test.

if(  BIT(3,value) )

where BIT is the function as we both mentioned:

#define BIT(i, status)       (((unsigned long)status & (1 << i))!=0) 

so when  i = 3  from above table will be be the word value as shown & with the Status1 bit pattern to test for OOS is true or not.

if Status 1 bit 3 = 1 then execute the If statement will be true, else go to the next one, etc.