Datasheet

PIC18F46J11 FAMILY
DS39932D-page 370  2011 Microchip Technology Inc.
23.1 Configuring the Comparator
Voltage Reference
The comparator voltage reference module is controlled
through the CVRCON register (Register 23-1). The
comparator voltage reference provides two ranges of
output voltage, each with 16 distinct levels. The range
to be used is selected by the CVRR bit (CVRCON<5>).
The primary difference between the ranges is the size
of the steps selected by the CV
REF Selection bits
(CVR<3:0>), with one range offering finer resolution.
The equations used to calculate the output of the
comparator voltage reference are as follows:
EQUATION 23-1: CALCULATING OUTPUT
OF THE COMPARATOR
VOLTAGE REFERENCE
The comparator reference supply voltage can come
from either V
DD and VSS, or the external VREF+ and
V
REF- that are multiplexed with RA2 and RA3. The
voltage source is selected by the CVRSS bit
(CVRCON<4>).
The settling time of the comparator voltage reference
must be considered when changing the CV
REF
output (see Table 29-4 in Section 29.0 “Electrical
Characteristics”).
When CVRR = 1 and CVRSS = 0:
CVREF = ((CVR<3:0>)/24) x (AVDD - AVSS)
When CVRR =
0 and CVRSS = 0:
CVREF =((AVDD - AVSS)/4) + ((CVR<3:0>)/32) x (AVDD - AVSS)
When CVRR =
1 and CVRSS = 1:
CVREF = ((CVR<3:0>)/24) x ((VREF+) – VREF-)
When CVRR =
0 and CVRSS = 1:
CVREF = (((VREF+) – VREF-)/4) + ((CVR<3:0>)/32) x ((VREF+)
– V
REF-)
REGISTER 23-1: CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER
(BANKED F53h)
R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0 R/W-0
CVREN CVROE
(1)
CVRR CVRSS CVR3 CVR2 CVR1 CVR0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 CVREN: Comparator Voltage Reference Enable bit
1 =CV
REF circuit powered on
0 =CV
REF circuit powered down
bit 6 CVROE: Comparator V
REF Output Enable bit
(1)
1 =CVREF voltage level is also output on the RA2/AN2/VREF-/CVREF/C2INB pin
0 =CV
REF voltage is disconnected from the RA2/AN2/VREF-/CVREF/C2INB pin
bit 5 CVRR: Comparator V
REF Range Selection bit
1 = 0 to 0.667 CV
RSRC, with CVRSRC/24 step size (low range)
0 = 0.25 CV
RSRC to 0.75 CVRSRC, with CVRSRC/32 step size (high range)
bit 4 CVRSS: Comparator V
REF Source Selection bit
1 = Comparator reference source, CV
RSRC = (VREF+) – (VREF-)
0 = Comparator reference source, CV
RSRC = AVDD – AVSS
bit 3-0 CVR<3:0>: Comparator VREF Value Selection bits (0  (CVR<3:0>)  15)
When CVRR =
1:
CVREF = ((CVR<3:0>)/24)  (CVRSRC)
When CVRR =
0:
CVREF = (CVRSRC/4) + ((CVR<3:0>)/32)  (CVRSRC)
Note 1: CVROE overrides the TRIS bit setting.