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April 19th, 2019, 04:33 AM   #1
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How to take this variable out of this equation?

I'm working to develop a function in my embedded code for i2c initialization.

I came up to this equation which is to calculate the speed of the i2c clock.

But if I want to develop a function that takes a user popular numbers for speed then I have to change the shape of the equation to get that variable in place to receive users values for adjusting the speed.

This is the equation:



I want to take out TWBR instead of SCL frequency. I tried to do it on a paper but I don't know how to take it out, from the multiple PrescalerValue and the addition of 16??!
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April 19th, 2019, 05:09 AM   #2
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OK, I solved it finally

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April 19th, 2019, 06:01 AM   #3
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$TWBR = \dfrac{(\text{CPU clock freq})- 16(\text{SCL freq})}{2(\text{SCL freq})(\text{Prescaler})}$
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April 19th, 2019, 07:45 AM   #4
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Quote:
Originally Posted by wolfrose View Post
I came up to this equation . . .
How?
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April 19th, 2019, 09:14 AM   #5
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Quote:
Originally Posted by wolfrose View Post
Yikes! Sure hope you assigned 1 letter variables to those; like:
a = SCL freq
b = CPU clock freq
c = TWBR
d = Prescaler Value

So you start with:
a = b / (16 + 2cd)

Then you can easily solve for b or c or d:

a = b / (16 + 2cd)
b = a(2cd + 16)

a = b / (16 + 2cd)
a(16 + 2cd) = b
16a + 2acd = b
2acd = b - 16a ****
c = (b - 16a) / (2ad)

2acd = b - 16a ****
d = (b - 16a) / (2ac)

EDIT:
your solution c = b / (2ad) is wrong....

Last edited by Denis; April 19th, 2019 at 09:31 AM.
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