PIC18F2480 MICROCHIP [Microchip Technology], PIC18F2480 Datasheet - Page 265

• Manufacturer Part Number: PIC18F2480
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 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 is of the module shown in
Figure 21-1.The resistor ladder is segmented to
provide two ranges of CV
power-down function to conserve power when the
reference is not being used. The module’s supply
reference can be provided from either device V
or an external voltage reference.
21.1
The voltage reference module is controlled through the
CVRCON register (Register 21-1). The comparator
voltage reference provides two ranges of output
REGISTER 21-1:
 2004 Microchip Technology Inc.
COMPARATOR VOLTAGE
REFERENCE MODULE
Configuring the Comparator
Voltage Reference
bit 7
bit 6
bit 5
bit 4
bit 3-0
CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL 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 = 0.00 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<0> bit setting. If enabled for output, RA2 must also
REF
REF
REF
REF
REF
REF
REF
= ((CVR3:CVR0)/24) (CV
= (CV
values and has a
circuit powered on
circuit powered down
voltage level is also output on the RA0/AN0/CV
voltage is disconnected from the RA0/AN0/CV
CVROE
be configured as an input by setting TRISA<2> to ‘1’.
RSRC
RSRC
RSRC
R/W-0
to 0.75 CV
to 0.75 CV
/4) + ((CVR3:CVR0)/32) (CV
(1)
PIC18F2480/2580/4480/4580
REF
REF
DD
REF
R/W-0
CVRR
/V
Range Selection bit
Preliminary
Source Selection bit
Output Enable bit
SS
W = Writable bit
‘1’ = Bit is set
REF
RSRC
RSRC
Value Selection bits (0
, with CV
, with CV
RSRC
CVRSS
R/W-0
RSRC
RSRC
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
(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
(see
Characteristics”).
)
REF
RSRC
RSRC
= (V
= V
If CVRR = 1:
CV
If CVRR = 0:
CV
CV
- that are multiplexed with RA2 and RA3. The
(1)
REF
REF
RSRC
Table 27-3
DD
selected
/24 step size
/32 step size
REF
RSRC
R/W-0
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
CVR3
– V
= ((CVR3:CVR0)/24) x CV
+) – (V
= (CV
)
DD
)
SS
and V
(CVR3:CVR0)
DD
REF
REF
by
REF
x 1/4) + (((CVR3:CVR0)/32) x
in
R/W-0
CVR2
pin
-)
SS
pin
the
, or the external V
Section 27.0
CV
x = Bit is unknown
REF
R/W-0
CVR1
15)
DS39637A-page 263
RSRC
Selection
“Electrical
REF
REF
R/W-0
CVR0
output
+ and
bit 0
bits