PIC18F1230 MICROCHIP [Microchip Technology], PIC18F1230 Datasheet - Page 179

• Manufacturer Part Number: PIC18F1230
• Description: 18/20/28-Pin, Enhanced Flash Microcontrollers with nanoWatt Technology, High-Performance PWM and A/D
• Manufacturer: MICROCHIP [Microchip Technology]

17.0
The comparator voltage reference is a 16-tap resistor
ladder network that provides a selectable reference
voltage. Its purpose is to provide a reference for the
analog comparators.
A block diagram of the module is shown in Figure 17-1.
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
17.1
The voltage reference module is controlled through the
CVRCON register (Register 17-1). The comparator
voltage reference provides two ranges of output
voltage, each with 16 distinct levels. The range to be
REGISTER 17-1:
© 2006 Microchip Technology Inc.
bit 7
Legend:
R = Readable bit
-n = Value at POR
bit 7
bit 6
bit 5
bit 4
bit 3-0
CVREN
R/W-0
REF
COMPARATOR VOLTAGE
REFERENCE MODULE
Configuring the Comparator
Voltage Reference
values and has a power-down function to
DD
CVREN: Comparator Voltage Reference Enable bit
1 = CV
0 = CV
Unimplemented: Read as ‘0’
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
/V
SS
REF
REF
U-0
—
or an external voltage reference.
CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER
= ((CVR3:CVR0)/24) (CV
= (CV
REF
REF
circuit powered on
circuit powered down
RSRC
RSRC
W = Writable bit
‘1’ = Bit is set
R/W-0
CVRR
/4) + ((CVR3:CVR0)/32) (CV
RSRC
to 0.75 CV
REF
REF
, with CV
Range Selection bit
Source Selection bit
Advance Information
REF
RSRC
CVRSS
R/W-0
RSRC
Value Selection bits (0
, with CV
RSRC
/24 step size (low range)
RSRC
RSRC
)
RSRC
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
= (V
= AV
R/W-0
CVR3
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 AV
multiplexed with RA4 and AV
selected by the CVRSS bit (CVRCON<4>).
The settling time of the comparator voltage reference
must be considered when changing the CV
Characteristics”).
output (see Table 22-3 in Section 22.0 “Electrical
/32 step size (high range)
REF
RSRC
DD
If CVRR = 1:
CV
If CVRR = 0:
CV
CV
+) – (AV
– AV
)
REF
REF
RSRC
selected
PIC18F1230/1330
SS
(CVR3:CVR0)
= (CV
= ((CVR3:CVR0)/24) x CV
)
SS
DD
R/W-0
CVR2
)
RSRC
or AV
by
SS
x 1/4) + (((CVR3:CVR0)/32) x
the
, or the external V
x = Bit is unknown
15)
SS
R/W-0
CVR1
CV
. The voltage source is
REF
DS39758B-page 177
RSRC
selection
REF
R/W-0
CVR0
+ that is
bit 0
REF
bits