Datasheet

 2010-2015 Microchip Technology Inc. DS40001303H-page 273
PIC18F2XK20/4XK20
21.2 FVR Reference Module
The FVR reference is a stable Fixed Voltage
Reference, independent of V
DD, with a nominal output
voltage of 1.2V. This reference can be enabled by
setting the FVREN bit of the CVRCON2 register to ‘1’.
The FVR defaults to on when any one or more of the
HFINTOSC, HLVD, BOR or ADC input channel
selection functions are enabled. The FVR voltage
reference can be routed to the comparators or an ADC
input channel.
21.2.1 FVR STABILIZATION PERIOD
When the Fixed Voltage Reference module is enabled, it
will require some time for the reference and its amplifier
circuits to stabilize. The user program must include a
small delay routine to allow the module to settle. The
FVRST stable bit of the CVRCON2 register also indicates
that the FVR reference has been operating long enough
to be stable. See Section 26.0 “Electrical
Specifications” for the minimum delay requirement.
FIGURE 21-1: VOLTAGE REFERENCE BLOCK DIAGRAM
16-to-1 MUX
CVR<3:0>
8R
R
CVREN
CVRSS = 0
V
DD
VREF+
CVRSS = 1
8R
CVRSS = 0
V
REF-
CVRSS = 1
R
R
R
R
R
R
16 Steps
CVRR
CVREF
1.2 Volt Fixed
Reference
EN
FVRST
FVR
FVREN
From HVLD, BOR circuits
and ADC channel selection
(CHS<3:0> = 1111)