Read out the value of the first 25 bits of a DINT value S7-1200 Tia portal

[smf]

Hi


I have a value stored within the first 25 bits of a DINT value and i'm wondering how to move/extract those 25 bits to another DINT?


I'm using tia portal 15.1 with s7-1200

 

[cardosocea]

You can copy the value to the "other" DINT and AND it with 177777777 to clear the high level bits.

 

[BryanG]

You need to know some Binary maths and how Siemens represents numbers of different base types, the simplest way to understand is to keep everything in binary format with 0s and 1s. As cardosocea said you create a mask, a mask here is just like a mask in photo editing, it lets some bits through and hides the rest. To create a 25 bit mask you declare a 32 bit double word and give it a value like this in SCL:

doubleWordVariable := 2#0000_0001_1111_1111_1111_1111_1111_1111;

'AND' that with your original number and only the values where there are 1s in the mask will keep there original values, the rest are set to 0.

http://www.plcdev.com/step_7_elementary_data_types


You could have declared the mask using hexadecimal using

doubleWordVariable := W#16#*01FFFFFF

cardosocea had his mask in Octal, not sure how you write that in Siemens terminology.
The zeros in my mask aren't needed, they just help me to understand.


Windows calculator has a Programmer setting that allows easy conversion between number Bases. Go to the 3 lines top left and choose 'Programmer'.

‬

 

[smf]

Great stuff and fast answers, thanks BryanG and cardosocea!


I'm a ladder guy, not used to doing stuff like this at all so i'll give it a try and return here if i fail

 

[cardosocea]

cardosocea had his mask in Octal, not sure how you write that in Siemens terminology.
‬

Ups... I was in a bit of a rush in the morning and didn't notice the Octal setting on the calculator. Thanks for the correction.

 

[JesperMP]

I have a value stored within the first 25 bits of a DINT value

With "first 25 bits", do you mean when reading the bits from the left (starting with the MSB) or do you mean when reading the bits from the right (starting with the LSB) ?

 

[smf]

With "first 25 bits", do you mean when reading the bits from the left (starting with the MSB) or do you mean when reading the bits from the right (starting with the LSB) ?

Bits 0 to 24 contains the data i want . So i guess from the right
?
The mask provided from BryanG seems to work so he was spot on.

 

[JesperMP]

Ok, just wanted to be sure.
Because of the arabs, numbers increase from right-to-left.
But when we read some text, it goes from left-to-right.
So "first 25 bits" can be interpreted both ways.

 

[Lare]

You can also do same on ladder with SHL and SHR commands (Shift left and then back to right 7bits of Dint)

 

[mk42]

Bits 0 to 24 contains the data i want . So i guess from the right
?
The mask provided from BryanG seems to work so he was spot on.

Since you mentioned being a LAD guy above, there is an AND instruction in LAD as well, under Basic Instructions -> Word Logic Operations.