PIC18F2682-I/PT MICROCHIP [Microchip Technology], PIC18F2682-I/PT Datasheet - Page 265

• Manufacturer Part Number: PIC18F2682-I/PT
• 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
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
REGISTER 21-1:
© 2007 Microchip Technology Inc.
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
bit 6
bit 5
bit 4
bit 3-0
Note 1:
Note:
CVREN
R/W-0
REF
COMPARATOR VOLTAGE
REFERENCE MODULE
Configuring the Comparator
Voltage Reference
values and has a power-down function to
CVROE overrides the TRISA<0> bit setting. If enabled for output, RA2 must also be configured as an
input by setting TRISA<2> to ‘1’.
Comparators are only available in 40/44-pin
devices (PIC18F4682/4685).
DD
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
/V
CVROE
SS
REF
REF
R/W-0
or an external voltage reference.
CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER
= ((CVR3:CVR0)/24) • (CV
= (CV
REF
REF
REF
REF
(1)
circuit powered on
circuit powered down
voltage level is also output on the RA0/AN0/CV
voltage is disconnected from the RA0/AN0/CV
RSRC
RSRC
RSRC
W = Writable bit
‘1’ = Bit is set
to 0.75 CV
to 0.75 CV
R/W-0
CVRR
/4) + ((CVR3:CVR0)/32) • (CV
REF
REF
REF
Range Selection bit
Source Selection bit
Output Enable bit
REF
RSRC
RSRC
PIC18F2682/2685/4682/4685
CVRSS
R/W-0
Value Selection bits (0 ≤ (CVR3:CVR0) ≤ 15)
, with CV
, with CV
RSRC
Preliminary
RSRC
RSRC
)
RSRC
RSRC
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
= (V
= V
(1)
R/W-0
CVR3
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”).
/24 step size
/32 step size
DD
REF
REF
RSRC
– V
If CVRR = 1:
CV
If CVRR = 0:
CV
CV
- that are multiplexed with RA2 and RA3. The
+) – (V
)
SS
REF
REF
RSRC
Table 27-3
selected
REF
= ((CVR3:CVR0)/24) x CV
REF
= (CV
REF
)
DD
R/W-0
CVR2
pin
-)
pin
and V
DD
by
x 1/4) + (((CVR3:CVR0)/32) x
in
SS
the
, or the external V
x = Bit is unknown
Section 27.0
R/W-0
CVR1
CV
REF
DS39761B-page 263
RSRC
selection
“Electrical
REF
R/W-0
CVR0
REF
output
+ and
bit 0
bits