PIC18F6585 Datasheet, PDF (267/496 Pages) Microchip Technology – 64/68/80-Pin High-Performance, 64-Kbyte Enhanced Flash Microcontrollers with ECAN Module

PIC18F6585/8585/6680/8680
21.0 COMPARATOR VOLTAGE
REFERENCE MODULE
The comparator voltage reference is a 16-tap resistor
ladder network that provides a selectable voltage
reference. The resistor ladder is segmented to provide
two ranges of CVREF values and has a power-down
function to conserve power when the reference is not
being used. The CVRCON register controls the
operation of the reference as shown in Register 21-1.
The block diagram is given in Figure 21-1.
The comparator reference supply voltage can come
from either VDD or VSS, or the external VREF+ and
VREF- that are multiplexed with RA3 and RA2. The
comparator reference supply voltage is controlled by
the CVRSS bit.
REGISTER 21-1:
CVRCON REGISTER
R/W-0 R/W-0 R/W-0
CVREN CVROE CVRR
bit 7
21.1 Configuring the Comparator
Voltage Reference
The comparator voltage reference can output 16 distinct
voltage levels for each range. The equations used to
calculate the output of the comparator voltage reference
are as follows:
If CVRR = 1:
CVREF = (CVR<3:0>/24) x CVRSRC
If CVRR = 0:
CVREF = (CVDD x 1/4) + (CVR<3:0>/32) x CVRSRC
The settling time of the comparator voltage reference
must be considered when changing the CVREF output
(Section 27.0 “Electrical Characteristics”).
R/W-0
CVRSS
R/W-0
CVR3
R/W-0
CVR2
R/W-0
CVR1
R/W-0
CVR0
bit 0
bit 7
bit 6
bit 5
bit 4
bit 3-0
CVREN: Comparator Voltage Reference Enable bit
1 = CVREF circuit powered on
0 = CVREF circuit powered down
CVROE: Comparator VREF Output Enable bit⁽¹⁾
1 = CVREF voltage level is also output on the RF5/AN10/C1IN+/CVREF pin
0 = CVREF voltage is disconnected from the RF5/AN10/C1IN+/CVREF pin
CVRR: Comparator VREF Range Selection bit
1 = 0.00 CVRSRC to 0.625 CVRSRC with CVRSRC/24 step size
0 = 0.25 CVRSRC to 0.71875 CVRSRC with CVRSRC/32 step size
CVRSS: Comparator VREF Source Selection bit
1 = Comparator reference source, CVRSRC = VREF+ – VREF-
0 = Comparator reference source, CVRSRC = VDD – VSS
Note:
To select (VREF+ – VREF-) as the comparator voltage reference source, the voltage
reference configuration bits in the ADCON1 register (ADCON1<5:4>) must also be
set to ‘11’.
CVR3:CVR0: Comparator VREF Value Selection bits (0 ≤ VR3:VR0 ≤ 15)
When CVRR = 1:
CVREF = (CVR<3:0>/24) • (CVRSRC)
When CVRR = 0:
CVREF = 1/4 • (CVRSRC) + (CVR3:CVR0/32) • (CVRSRC)
Note 1: If enabled for output, RF5 must also be configured as an input by setting TRISF<5>
to ‘1’.
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
 2004 Microchip Technology Inc.
DS30491C-page 265