Pointers in Step 7...

[Borte]

Hello everybody!

I have a question regarding pointers in step7...

As far as I see this is some of the harder things to understand using the S7 plc's. I've been reading the Siemens help on "pointers" and "any" and I've been using dynamic "pointers" (buildt my own) in the past. So I know what to put in what byte and so on to make it work. But I'm still confused about what to use when. Like what is the real difference between "any" and "pointer" and when to use them? Usually I use "any" but...??? Ah... just confused!

Also according to the Siemens help file I can add a number to the AR1 using the +AR1 command, but what does this do? How can I use it? Will it change the byte address or will it change the bit number..

So input would be helpful.

Regards
Borte

 

[Ken M]

Hi Borte


Well, I'll bet you get lots of replies on this topic! And every one will have their own ideas!

The difference between a POINTER and an ANY data type? A POINTER just identifies a memory location - it 'points' to an address somewhere. An ANY data type adds to this by allowing you to identify the type of data and the amount of data to be found at that address. So for example a POINTER could identify 'DB20.DBB20' and nothing else would be known. Any ANY could identify '6 REALS starting at DB20.DBB20'

When to use them? Well, it depends on what you want to do. Do you need to refer to a quantity of data or just a data location?

The AR1 contents only represent a portion of a full POINTER or ANY. It is only 32-bits long and can hold the memory area (M, I, Q, DB etc) plus byte and bit address. Yes, you can adjust the values here by addition or subtraction etc. And as a result you can alter the location to which the POINTER points.

Just some ideas to start with ... Let's see how this develops.

Ken.

 

[SimonGoldsworthy]

Borte - Please give a specific example of what you want to do.

 

[Super_unknown]

Would have given a reply but am confused myself..
Can I use pointers say for example as a Shift register?
Can anybody give an example on how to use pointers in shift register applications? thanks..