Re: [Gumstix-users] Difference betwwen methods of ADC

[Dave H. <dhy...@gm...>]

Hi Tracy,

> I used to use the getADC command using I2C, however, I recently changed to
> using a2d_10.c. The weird thing is they give me different results. As far as
> I can see, both make use of ADCH and ADCL so surely they must give the same
> readings? What is the difference and would there be any reason to use the
> one or the other? Also how can I make a2d_10.c give me the same readings as
> getADC?

What is the getADC command that you're referring to?

Some A/D functions return an 8-bit value, and some return a 10-bit value.

The ADLAR bit determines if the 10 bit result is in the leftmost 10
bits or the rightmost 10 bits of the 16-bit ADC register. Normally,
when reading 8-bit values, you would set ADLAR=1 and just use ADCH
which will return the most significant 8-bits of the 10-bit result.

Are the REFS0 and REFS1 bits set the same in both cases? Obviously
changing the reference voltage used will change the result.

-- 
Dave Hylands
Vancouver, BC, Canada
http://www.DaveHylands.com/