Accessing bits in a REAL in Logix Designer

zacslade · Apr 20, 2016

Hi all,

This has been bugging me for some time, but it is only recently advantageous for me to have an answer. I know that REAL values are designed to be used for analog values, but that they are ultimately stored as binary.

I am working on a 1769-L33ER in Logix Designer, and I want to access the bits in a REAL tag. Is there any way to do it?

Thanks!

ASF · Apr 20, 2016

I don't think there is. I've had that thought before too, and had a look to see if there's a way to do it, and never found one.

Having said that, I'm going to lurk here and watch for a while, because if anyone has done it, this will be where you find them

One question though - what's the situation that's made it "advantageous for you to have an answer"? I'm curious

zacslade · Apr 20, 2016

ASF said:
One question though - what's the situation that's made it "advantageous for you to have an answer"? I'm curious

Haha - It's not terribly advantageous, just a little.

I am pulling a large number of tags from a single modbus device, through a Redlion DSPLE. Since Redlion's Crimson software doesn't import the AOIs I'm using, I figured I'd make a large array to hold all the raw values, and then map them to the AOIs.

All but two of the values I'm pulling in are IEEE 754 Floating Point, so I had to make another tag to hold those last two integers.

It ruined my tag structure.

ASF · Apr 20, 2016

zacslade said:
All but two of the values I'm pulling in are IEEE 754 Floating Point, so I had to make another tag to hold those last two integers. It ruined my tag structure.

You know, I think you and I would get along well!

Ron Beaufort · Apr 20, 2016

not sure exactly what you're trying to accomplish - but you might want to try this idea ...

use a COP (Copy) instruction to take a REAL number and copy it into a DINT location ... you should be able to address/access the individual bits within the DINT ...

SECRET HANDSHAKE: a MOV instruction moves a VALUE ... a COP instruction on the other hand moves BIT PATTERNS ...

DISCLAIMER: I don't have a Logix system handy here at home - but I know that I've done this before with the older platforms ...

kamenges · Apr 20, 2016

Originally posted by Ron Beaufort[/b]:

DISCLAIMER: I don't have a Logix system handy here at home - but I know that I've done this before with the older platforms ...

Yep, still works.

But I'm still not sure why you want direct access to the individual bits.

Keith

Mark- · Apr 20, 2016

Hello,

zacslade said:
...but that they are ultimately stored as binary.

Not to be pedantic; "stored as binary" could be interpreted as "bit weighted" or each bit has a value and all the bits added together have a value.

Floating point numbers are encoded. IEEE 754 is a common encoding.

So, floating point numbers are not really stored as binary. They are values that are encoded and saved.

Depending on why you want to access some part of the encoding, there might be much easier/faster/cleaner methods.

You might know all the above. If so, never mind.

My2c.

AustralIan · Apr 21, 2016

Code:

COP MyReal MyDint 1
XIC MyDint.[MyIndex] OTE BitOneIsOn

You could roll this into an AOI to access the bit if you don't want to add a program or controoler scoped tag

zacslade · Apr 21, 2016

Wow, thanks! That seemed to have worked.

You guys are awesome.

Accessing bits in a REAL in Logix Designer

zacslade

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