At 02:58 PM 23/11/2011, you wrote:
>I was planning to use the internal CVREF on the 18F26K20, but I'm
>confused by microchip's documentation. On page 291:
>
>CVRR: Comparator VREF Range Selection bit
>1 =3D 0 to 0.667 CVRSRC, with CVRSRC/24 step size (low range)
>0 =3D 0.25 CVRSRC to 0.75 CVRSRC, with CVRSRC/32 step size (high range)
>
>When CVRR =3D 1:
>CVREF =3D ((CVR<3:0>)/24) * (CVRSRC) + VREF-
>When CVRR =3D 0:
>CVREF =3D (CVRSRC/4) + ((CVR<3:0>)/32) * (CVRSRC) + VREF-
>
>With 4 bits, 15 being the maximum CVR value, how can you get .667
>CVRSRC? I get the value of .625 CVRSRC max.
>When CVRR =3D 0, I again get 0.71875 CVRSRC and not .75 as advertised.
>
>It looks like they plugged 16 into the formula to get .667 or .75
>CVRSRC values.
>
>The datasheet in question is available here:
>http://ww1.microchip.com/downloads/en/DeviceDoc/41303G.pdf
>
>I haven't tried it in circuit yet, or looked at any other datasheets.

Your numbers are correct, based on figure 21-1 as well as the
numbers in the Midrange Reference Manual (Table 19-1), which shows
a voltage of 3.13 V with VRR=3D1 and 1111 for VR3:VR0 (Vdd =3D 5.0V)

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the rewar=
d"
speff@interlog.com             Info for manufacturers: http://www.trexon.co=
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