CODEWITHSUNDEEP
cmicrocontrollerfixed-point
Corono
Corono

Reputation: 35

Unsigned fixed point 0.28 format

I found in a stepper driver datasheet L6472 the following description:

enter image description here

What is the "unsigned fixed point 0.28 format"?

I found information about the fixed point format itself, but what does the 0.28 mean?

Is there an easy implementation for this conversion from [step/s] to SPEED in C on a micro-controller without floating point unit?

Upvotes: 3

Views: 697

Answers (1)

Eric Postpischil
Eric Postpischil

Reputation: 223814

The notation m.n for a fixed-point format means there are m bits representing an integer portion of a number and n bits represent a fractional portion of a number.

If you have m+n bits interpreted as some integer N, then the same bits would be interpreted as an m.n fixed-point number N/2n.

So, if you have 28 bits that, when interpreted as an integer, represent a value of N, then, when interpreted as a 0.28 fixed-point number, they represent a value of N/228.

Note that it is unusual for a register to have only 28 bits. If the register actually has 32 bits, then the high four bits should be ignored when interpreted the contents as a 0.28 fixed-point number, unless it is known they must be zero.

Upvotes: 4

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