PIC18F6525_13 Datasheet, PDF (249/400 Pages) Microchip Technology – 64/80-Pin High-Performance, 64-Kbyte Enhanced Flash Microcontrollers with A/D

PIC18F6525/6621/8525/8621
22.0 COMPARATOR VOLTAGE
REFERENCE MODULE
The comparator voltage reference is a 16-tap resistor
ladder network that provides a selectable voltage
reference. The resistor ladder is segmented to provide
two ranges of CVREF values and has a power-down
function to conserve power when the reference is not
being used. The CVRCON register controls the
operation of the reference as shown in Register 22-1.
The block diagram is given in Figure 22-1.
The comparator reference supply voltage can come
from either VDD and VSS, or the external VREF+ and
VREF- that are multiplexed with RA3 and RA2. The
comparator reference supply voltage is controlled by
the CVRSS bit.
22.1 Configuring the Comparator
Voltage Reference
The comparator voltage reference can output 16
distinct voltage levels for each range. The equations
used to calculate the output of the comparator voltage
reference are as follows:
If CVRR = 1:
CVREF = (CVR<3:0>/24) x CVRSRC
If CVRR = 0:
CVREF=(CVRSRC x 1/4)+(CVR<3:0>/32)xCVRSRC
The settling time of the comparator voltage reference
must be considered when changing the CVREF output
(Section 27.0 “Electrical Characteristics”).
REGISTER 22-1:
CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER
R/W-0 R/W-0 R/W-0
CVREN CVROE⁽¹⁾ CVRR
R/W-0
CVRSS
R/W-0
CVR3
R/W-0
CVR2
R/W-0
CVR1
R/W-0
CVR0
bit 7
bit 0
bit 7
bit 6
bit 5
bit 4
bit 3-0
CVREN: Comparator Voltage Reference Enable bit
1 = CVREF circuit powered on
0 = CVREF circuit powered down
CVROE: Comparator VREF Output Enable bit⁽¹⁾
1 = CVREF voltage level is also output on the RF5/AN10/CVREF pin
0 = CVREF voltage is disconnected from the RF5/AN10/CVREF pin
Note 1: If enabled for output, RF5 must also be configured as an input by setting TRISF<5>
to ‘1’.
CVRR: Comparator VREF Range Selection bit
1 = 0.00 CVRSRC to 0.667 CVRSRC, with CVRSRC/24 step size (low range)
0 = 0.25 CVRSRC to 0.75 CVRSRC, with CVRSRC/32 step size (high range)
CVRSS: Comparator VREF Source Selection bit
1 = Comparator reference source, CVRSRC = VREF+ – VREF-
0 = Comparator reference source, CVRSRC = AVDD – AVSS
CVR3:CVR0: Comparator VREF Value Selection bits (0  VR3:VR0  15)
When CVRR = 1:
CVREF = (CVR<3:0>/ 24)  (CVRSRC)
When CVRR = 0:
CVREF = 1/4  (CVRSRC) + (CVR3:CVR0/32)  (CVRSRC)
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
 2003-2013 Microchip Technology Inc.
DS39612C-page 249