24 bit 2's complement hex string to number

[ajapyy]

i get a 24 bit 2's complement hex number in string format from serial port. i want use this hex number in continue in my LabVIEW code. but it doesn't work correctly !!

in example if i receive ffffff it is equal to -1 and if i receive 000001 it is equal to +1 .

anybody has solution for my problem ?

Thanks.

[JB]

See here.

[GerdW]

As JB's link doesn't work for me (right now as NI website seems to have its problems) I attach this snippet:

[ajapyy]

Thank you friends.

but finally i want a number that can be positive or negative. in fact i need number in DBL format with it's sign.

[GerdW]

Hi ajapyy,

an I32 is sufficient here as it also keeps the sign (and your "hex number" doesn't come with fractional digits).

You are free to convert the I32 to DBL later on…

[JLewis]

That's a pretty clever sign extension, but a little difficult for me to wrap my brain around. An alternative to let LV do it for you would be to use a 24-bit fixed-point type for the conversion:

[GerdW · Accepted solution]

Hi JLewis,

get the sign bit, multiply it by 2*255 to fill the upper 8 bits of the I32, OR it with the remaining bits of the number…

[JB]

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JLewis a écrit :

That's a pretty clever sign extension, but a little difficult for me to wrap my brain around. An alternative to let LV do it for you would be to use a 24-bit fixed-point type for the conversion:

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Very interesting ! This is the first time I see this solution.

[Hong.Zhang@agresearch.co.]

Hi All

I am trying to converter 4 bit hex string to number. I know the right results. But I do not know how converte. Please see the attached vi

Please help me.

Thanks

[GerdW]

Hi Hong,

please convert your VI to LV2011. Do you mind to write down some example numbers?

And what is a "4 bit hex string"?