STL bit and byte numbers

Avatar_41 · May 22, 2023

Hello everyone, friends. I need help with something. I want to read and change Bit and Byte numbers via HMI. I found a code snippet for this as below. I tried, it works, but I don't know how to transfer the values like "I 10.7" that I marked in red here to another address and read and change it. I need your support on this.

L D[AR2P#0.0] · May 23, 2023

When you say you tried it, it works, what do you mean by that as your code is not writing the output_bit?

cardosocea · May 23, 2023

There's a document from Siemens laying out how the pointer is formed, and the memory area it points to is a number in the address formed. I reckon it's the 810000000 number that commands this. search the help for pointer and it's likely there the explanation.

cardosocea · May 23, 2023

Also, STL is on its way out, I'd instead look at pointing to an IO buffer instead.

Avatar_41 · May 23, 2023

I may not have explained exactly what I want to do. Translation problems may occur. Bit and Byte numbers appear in LAR1, for example I 10.7. I want to transfer the 10.7 value here to a DataBlock address and change it whenever I want via the HMI. However, I don't know how to pass this value to DataBlock and I need help with this.

L D[AR2 said:
When you say you tried it, it works, what do you mean by that as your code is not writing the output_bit?

cardosocea · May 24, 2023

I understood what you wanted to do perfectly. You'd want a box to write the byte number and another box to write the bit number. and then return the value at that memory position.

And the way to do this is via addressing with a pointer.

Check here:

https://www.fleaplc.it/index.php/tutorials/6-simatic-step7-any-pointer-input-parameter

Search the help for:

Format of the Parameter Type Pointer

L D[AR2P#0.0] · May 24, 2023

Your example code already does what you want. Change the values in DB10 via the HMI to address a different byte/bit.

Avatar_41 · May 24, 2023

Here's the problem, I'm writing as 11.7 on the HMI, but I can't see this value as 11.7. However, if in the Watt table; If I choose Out Variable display format as Pointer, I can read it, but if I set the data type as Pointer in FC1, Out Variable turns red, so it goes into error. I couldn't understand how I could solve this.

L D[AR2 said:
Your example code already does what you want. Change the values in DB10 via the HMI to address a different byte/bit.

L D[AR2P#0.0] · May 25, 2023

Here's your code with byte number=11 and bit number=7, I can see I11.7 in the FC.

You need to post some screen shots to explain what you are looking at.

Manglemender · May 25, 2023

Avatar_41 said:
Here's the problem, I'm writing as 11.7 on the HMI, but I can't see this value as 11.7. However, if in the Watt table; If I choose Out Variable display format as Pointer, I can read it, but if I set the data type as Pointer in FC1, Out Variable turns red, so it goes into error. I couldn't understand how I could solve this.

There are two different types of pointer in S7. What you are creating is a byte pointer which is 4 bytes (DWORD). The other type of pointer is an ANY POINTER which is 10 bytes and has a complex structure.

Avatar_41 · May 26, 2023

When I select Any as the data type of Output, it goes into error.

Manglemender said:
There are two different types of pointer in S7. What you are creating is a byte pointer which is 4 bytes (DWORD). The other type of pointer is an ANY POINTER which is 10 bytes and has a complex structure.

Avatar_41 · May 26, 2023

I'm sorry to bother you all the time, but I think I'm doing something wrong. When I change the values via hmi, for example, when I type 0.0, the decimal value changes to -2130706432. When you do 0.1, it changes to -2130706431. Do I need to divide this number by another number to get ("I0.0")? Or do I need to do something else?

L D[AR2 said:
Here's your code with byte number=11 and bit number=7, I can see I11.7 in the FC.

You need to post some screen shots to explain what you are looking at.

L D[AR2P#0.0] · May 27, 2023

You are doing nothing wrong. What is the purpose of writing the area pointer to the OUTPUT?

Manglemender · May 27, 2023

Also, the two AND statements prior to the Transfer instruction have no effect on the Transfer so they serve no purpose. What was the intent for those instructions?

Avatar_41 · May 28, 2023

What I don't understand is: Why can't I see these 0.0 or 0.1 values, so what can I do to see 0.0 instead of -2130706432?

L D[AR2 said:
You are doing nothing wrong. What is the purpose of writing the area pointer to the OUTPUT?

STL bit and byte numbers

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