PIC18F2420 MICROCHIP [Microchip Technology], PIC18F2420 Datasheet - Page 241

• Manufacturer Part Number: PIC18F2420
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

21.0
The comparator voltage reference is a 16-tap resistor
ladder network that provides a selectable reference
voltage. Although its primary purpose is to provide a
reference for the analog comparators, it may also be
used independently of them.
A block diagram of the module is shown in Figure 21-1.
The resistor ladder is segmented to provide two ranges
of CV
conserve power when the reference is not being used.
The module’s supply reference can be provided from
either device V
21.1
The voltage reference module is controlled through the
CVRCON register (Register 21-1). The comparator
voltage reference provides two ranges of output volt-
age, each with 16 distinct levels. The range to be used
REGISTER 21-1:
 2004 Microchip Technology Inc.
REF
COMPARATOR VOLTAGE
REFERENCE MODULE
Configuring the Comparator
Voltage Reference
values and has a power-down function to
bit 7
bit 6
bit 5
bit 4
bit 3-0
DD
/V
SS
or an external voltage reference.
CVRCON REGISTER
bit 7
Legend:
R = Readable bit
-n = Value at POR
CVREN: Comparator Voltage Reference Enable bit
1 = CV
0 = CV
CVROE: Comparator V
1 = CV
0 = CV
CVRR: Comparator V
1 = 0 to 0.667 CV
0 = 0.25 CV
CVRSS: Comparator V
1 = Comparator reference source, CV
0 = Comparator reference source, CV
CVR3:CVR0: Comparator V
When CVRR = 1:
CV
When CVRR = 0:
CV
CVREN
R/W-0
Note 1: CVROE overrides the TRISA<2> bit setting.
REF
REF
= ((CVR3:CVR0)/24) (CV
= (CV
REF
REF
REF
REF
CVROE
circuit powered on
circuit powered down
voltage level is also output on the RA2/AN2/V
voltage is disconnected from the RA2/AN2/V
RSRC
RSRC
R/W-0
/4) + ((CVR3:CVR0)/32) (CV
RSRC
to 0.75 CV
(1)
PIC18F2420/2520/4420/4520
REF
REF
REF
, with CV
R/W-0
CVRR
Range Selection bit
Preliminary
Source Selection bit
Output Enable bit
W = Writable bit
‘1’ = Bit is set
REF
RSRC
RSRC
Value Selection bits (0
, with CV
RSRC
CVRSS
R/W-0
/24 step size (low range)
RSRC
RSRC
is selected by the CVRR bit (CVRCON<5>). The pri-
mary difference between the ranges is the size of the
steps
(CVR3:CVR0), with one range offering finer resolution.
The equations used to calculate the output of the
comparator voltage reference are as follows:
The comparator reference supply voltage can come
from either V
V
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
put (see Table 26-3 in Section 26.0 “Electrical
Characteristics”).
)
REF
RSRC
If CVRR = 1:
CV
If CVRR = 0:
CV
CV
= (V
= V
- that are multiplexed with RA2 and RA3. The
(1)
REF
REF
RSRC
selected
DD
/32 step size (high range)
REF
RSRC
R/W-0
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
CVR3
– V
= (CV
= ((CVR3:CVR0)/24) x CV
+) – (V
)
DD
)
SS
REF
and V
RSRC
(CVR3:CVR0)
REF
by
REF
-/CV
R/W-0
-/CV
CVR2
x 1/4) + (((CVR3:CVR0)/32) x
-)
SS
the
REF
, or the external V
REF
pin
CV
pin
x = Bit is unknown
REF
R/W-0
CVR1
15)
DS39631A-page 239
RSRC
Selection
REF
R/W-0
CVR0
REF
+ and
bit 0
out-
bits