S7 Pointer Question

adfox · Dec 6, 2011

Hi, i've came across this code:

Code:

   AN    #STATUS.R_REQ
      AN    #STATUS.R_BUSY
      S     #STATUS.R_REQ

      CALL  "RDSYSST"
       REQ       :=#STATUS.R_REQ
       SZL_ID    :=W#16#292
       INDEX     :=W#16#1
       RET_VAL   :=#STATUS.RET
       BUSY      :=#STATUS.R_BUSY
       SZL_HEADER:=#STATUS.SZL_HEADER
       DR        :=#Status_Profi_read

      A     #STATUS.R_REQ
      AN    #STATUS.R_BUSY
      R     #STATUS.R_REQ

      L     P##Status_Profi_read
      T     #PointerWrite
      L     DID [#PointerWrite]
      L     #PointerWrite
      L     P#4.0
      +D    
      T     #PointerWrite

Status_profi_read is an array of bools [0..127]
PointerWrite is Temp Dword. Code is in FB.

Function reads profibus nodes status and puts them into addressed array.

My question is: How does it work ?
No loop, no limitation for pointer ( if loop exceedes 32 DWORDS -> Start from DWORD 0 ), and yes - this function is working properly.

Can You point me in right direction ?

L D[AR2P#0.0] · Dec 6, 2011

adfox said:
My question is: How does it work ?
No loop, no limitation for pointer ( if loop exceedes 32 DWORDS -> Start from DWORD 0 ), and yes - this function is working properly.

Can You point me in right direction ?

Apart from the contradiction indicated above - without the rest of the code that follows there is not a lot that can be said.

adfox · Dec 7, 2011

L D[AR2 said:
Apart from the contradiction indicated above - without the rest of the code that follows there is not a lot that can be said.

And, that's the weird part - there's no rest of the code ;]
So i'm just asking how it works - because i can't get to understand the rule for the pointer loop.

The status of profibus nodes is written into appropriate array element...

CPU is running without any SF that would indicate addressing error, nothing - it's just there.

Ah, for the contradiction mentioned above-> Usually one can spot something when using indirect addressing like loop or resetting the pointer index - that was what I wanted to write - sorry.

L D[AR2P#0.0] · Dec 7, 2011

In that case the following code is redundant and was probably ony ever used for monitoring the array programatically

Code:

     L     P##Status_Profi_read
      T     #PointerWrite
      L     DID [#PointerWrite]
      L     #PointerWrite
      L     P#4.0
      +D    
      T     #PointerWrite

adfox · Dec 7, 2011

Could You explain little more ? How is this achieved ?

L D[AR2P#0.0] · Dec 7, 2011

By loading a pointer to Status_Profi_read, this code will continue to monitor the correct data even if the STAT data area is modified. (Note that this code will only work if this FB is called with it's own instance DB).

Here's the code being monitored with some test data:

adfox · Dec 7, 2011

Wow, again You're amaising ;] Thanks for light in the dark. More than 3 years with S7 and there is so much to learn, eh... where's the time for the rest of them.

Looking into variety of S7 coding standards, makes me feel that i don't know more than i know

Thanks!

(Note that this code will only work if this FB is called with it's own instance DB)

What do you mean by that ?

L D[AR2P#0.0] · Dec 7, 2011

It means you cannot use this coding method if the FB is called as a multiple instance from another FB.

STL??? · Dec 8, 2011

You should write a book on S7 programming LD - i'd buy it

adfox · Dec 9, 2011

Thanks, I'd buy it too

S7 Pointer Question

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