Dear sir,

I have little confusion in addressing of analog input.

When to use PIW, IW, PIB, PID ,QW etc....

Pls help ,

Regards,

Pankaj tiwari

Thankx for reply,

but what about PIB, PID ,QW????

Regards,

Pankaj Tiwari

pankaj_054

Thankx for reply,

but what about PIB, PID ,QW????

Regards,

Pankaj Tiwari

P : Peripheral (direct reading/writing)
I : Input (signal reading)
Q : Output (signal writing)
B : Byte size (8 bits)
W : Word size (16 bits)
D : Double word size (32 bits)

These were important for the older PLCs which had less resources than we have now.

The inputs and outputs that we use normally is something like I4.2 or IW10 or such. Those are inputs / outputs that are buffered; a memory area that is refreshed at regular times. This is by default updated every 1 scan but can be configured differently.

But there can be inputs / outputs that is outside the region of automatic refresh. For that you need another way to address them. You read directly from the input / output. Practically that is what the "P" tell us.

On older PLCs, even something as basic as analogs were outside the automatically updated range. An analog is represented by a 16-bit number. So the direct reading of an analog would be PIW300 (peripheral input of word size starting from at input byte address 300). The same idea applies to the outputs but also for communication devices linked to the input/output area.

Do know that it is possible in the hardware configuration to move the addresses into a region that is automatically updated. So before with PIW300 moved to a new address can then be access as for example IW20.

Do note that sometimes we need to read/write inputs/outputs immediately without waiting for the buffer to clear to the physical peripheral. In that case we could use for example PID0 which reads immediately the bits I0.0 up to I3.7. This is handy for usage in an interrupt routine.

Lastly -- Step7 under TIA Portal uses another notation. PID0 would become ID0:P  

Do these notes help?