Dynamic Determination of UDT Size

Rusty_K

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• May 30, 2005

• #1

Hello,

Does anyone know if it's possible to dynamically determine the size of a defined UDT in Step 7? Any help would be greatly appreciated.

Cheers

R.K.

 

S7Guy

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• May 30, 2005

• #2

Yes, you can determine the size of any complex variable by passing it into a function as a pointer. Take a look at this thread for details: http://www.plctalk.net/qanda/showthread.php?t=10741&highlight=udt

 

Borte

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• May 31, 2005

• #3

There is one problem with this though.... If you pass a db into a any input at a block the size of the area will be set to 2 bytes!! How exactly would you determine the complete size of the db?


Cheers
Borte

 

SimonGoldsworthy

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• May 31, 2005

• #4

L DBLG //load the length of current global data block (in bytes)

 

Borte

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• May 31, 2005

• #5

Thanks Simon!

I was not aware of that command, but how do you differentiate between the different types of pointers you could have in a "any" input?

Wheter or not the programmer used just DB100 or P#DB100.DBX10.0 BYTE 4??

I know how to sepearate the different types but not how to detect just a db input.

Cheers
Borte

 

SimonGoldsworthy

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• May 31, 2005

• #6

An any pointer for blocks has the type byte=19hex.e.g.

CALL FC 594
pPointer:=DB100
NOP 0

then FC594 is as follows (pPointer is an input parameter of type any):

L P##pPointer //values shown in hex
LAR1
L W [AR1,P#0.0] //=1019
L W [AR1,P#2.0] //=1
L W [AR1,P#4.0] //=0
L D [AR1,P#6.0] //=64

 

Borte

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• May 31, 2005

• #7

So then I have to check for type 19h then use the DBLG to find the size of the db?

What does the 64h in byte 6 stand for? I can't find anything about that in the help. Shouldn't it be 2 for byte?

 

SimonGoldsworthy

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• May 31, 2005

• #8

Borte said:

So then I have to check for type 19h then use the DBLG to find the size of the db?

What does the 64h in byte 6 stand for? I can't find anything about that in the help. Shouldn't it be 2 for byte?

Click to expand...

Yes, and 64hex = 100 decimal, this is the number of the DB.

 

Borte

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• May 31, 2005

• #9

Ahh... It has to be to early in the morning... I should have seen that... My mistake.

Thanks again

Cheers
Borte