S7 Adres registers

Werner · Aug 30, 2005

I have an FC.

Input: level_nr : INT
Output: Data : UDT9

In this FC I use indirect addressing to copy data from a DB to the output. When I'm looking online I see a V mark in the column of AR1. Does anybody know what this means?

It looks like:

--------------------------------AR1 AR2

OPN DB60 ----------------------0.0 92.0
L DBX[AR2,P#2.0]---------------0.0 92.0
T Data.Nr_batches ------------V 0.0 92.0

??????-------------------------^

SimonGoldsworthy · Aug 30, 2005

The 'V' area is the temporary local data area of the block that called the block you are monitoring.

Werner · Aug 30, 2005

Before I calculated a pointer on AR1. Does the V also mean that the AR1 register is overwriten by the temporary local data? With the pointer in AR1 the block wasn't working. Later I calculated a pointer in AR2, this seems to be working.

SimonGoldsworthy · Aug 30, 2005

If you use a UDT as a parameter in an FC, AR1 is used to access each element of the UDT. Note also that if the parameter exists in a DB, the DB is left open after the UDT parameter access.

jacekd · Aug 31, 2005

As a general rule you should store AR1/AR2 at very begining of your FC/FB and restore them at very end if you plan mess up with them. It will prevent your code in case of malfunction from hitting the rest of the program.

Borte · Aug 31, 2005

jacekd said:
As a general rule you should store AR1/AR2 at very begining of your FC/FB and restore them at very end if you plan mess up with them. It will prevent your code in case of malfunction from hitting the rest of the program.

I thought the plc automatically handles the AR1/2 when it jumps back into the calling block? I have played with both AR1 and 2 but I have never restored or had any problems with it (that I know of).

Cheers
Borte

SimonGoldsworthy · Aug 31, 2005

Have a look at this bit of code -

http://www.plctalk.net/qanda/showthread.php?p=104628&highlight=ar1#post104628

Werner · Aug 31, 2005

So if I understand correctly: (looking at the code posted by SimonGoldsworthy)

1. In an FC AR1 is overwritten when using temporary local data
2. In an FB AR2 is overwritten when using temporary local data

So this is very tricky! (Especially if you make a small change in a program that already worked, what I did.) But the rewards can be a very short piece of code...There's always a catch to it.

SimonGoldsworthy · Aug 31, 2005

In a FC, AR1 is overwritten when referencing a parameter of type UDT. This is not what you have written - is this what you meant ?

Werner · Aug 31, 2005

SimonGoldsworthy said:
In a FC, AR1 is overwritten when referencing a parameter of type UDT. This is not what you have written - is this what you meant ?

Yes, sorry. I'm used to Visual Basic. So it's hard to get into the indirect addressing of Siemens. All things that look normal to me can't be done with Siemens.

Example: L DB60.DBW[AR1,P#2.0]
or: L DB60.DBW[Index] (I know CSL could do this...)

jacekd · Sep 1, 2005

Werner said:
In an FB AR2 is overwritten when using temporary local data

In case of a FB the AR2 holds an offset of the IN/OUT/INOUT/STAT data (but no TEMP) in the instance DB.

Werner · Sep 5, 2005

In this function I copy data from an DB to the UDT at the output of the function. Why do I have to open the DB every time between a copy? See code below

Code:

OPN DB	60
A	 DBX [AR2,P#0.0]
=	 #Info.Empty
OPN DB	60
A	 DBX [AR2,P#0.1]
=	 #Info.Loading

The DB1 registers is set to zero when coping data to the UDT. If I don't open de DB I get area length error when reading. Is there an other solution to prevent this? (Maby try to open the DB in an other register? or first copy all data to temporary data (not in UDT) and then in the end copy to UDT?)

SimonGoldsworthy · Sep 5, 2005

Your instruction:

= #Info.Empty

will change AR1 and the DB1 register (if the value exists in a DB). The DB register is modified you must save the DB register before hand and then restore it afterwards. (From my testing, if Info.Empty is in the local data of the calling block, the DB register does not change - you would be unwise to rely on this though)

Werner · Sep 5, 2005

Is it possible to store the output of the function (The UDT) directly in an DB which also has the UDT defined in it? I tried to copy the output of the function with an ANY pointer to the DB. Unfortunately Siemens does not except my input! (P#DB16.DBX0.0 Byte 20)

SimonGoldsworthy · Sep 5, 2005

An alternative is to declare the UDT in the local data area and then do

OPN DB 60
A DBX [AR2,P#0.0]
= #Local.Empty
etc....

then
A #Local.Empty
= #Info.Empty
etc...

S7 Adres registers

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