PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 253

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

22.0
This module is a 16-tap resistor ladder network that
provides a selectable voltage reference. The resistor
ladder is segmented to provide two ranges of CV
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 22-1. The block
diagram is shown in Figure 22-1.
The comparator and reference supply voltage can
come from either V
and V
comparator reference supply voltage is controlled by
the CVRSS bit.
REGISTER 22-1:
Note:
2002 Microchip Technology Inc.
REF
COMPARATOR VOLTAGE
REFERENCE MODULE
-, that are multiplexed with RA3 and RA2. The
The Comparator Voltage Reference is only
available
PIC18F458.
bit 7
bit 6
bit 5
bit 4
bit 3-0
DD
and V
on
CVRCON REGISTER
bit 7
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
CVR<3:0>: Comparator V
When CVRR = 1:
CV
When CVRR = 0:
CV
Legend:
R = Readable bit
- n = Value at POR
CVREN
R/W-0
REF
REF
SS
the
REF
REF
REF
REF
, or the external V
= (CVR3:CVR0/24) (CV
= 1/4 (CV
PIC18F448
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
CVROE
R/W-0
to 0.625 CV
to 0.719 CV
RSRC
REF
REF
REF
) + (CVR3:CVR0/32) (CV
REF
R/W-0
CVRR
and
Range Selection bit
REF
REF
Preliminary
Source Selection bit
Output Enable bit
W = Writable bit
’1’ = Bit is set
+
RSRC
RSRC
Value Selection 0
RSRC
, with CV
, with CV
CVRSS
RSRC
RSRC
R/W-0
)
22.1
The Comparator Voltage Reference can output 16 dis-
tinct voltage levels for each range. The equations used
to calculate the output of the Comparator Voltage
Reference are as follows.
EQUATION 22-1:
EQUATION 22-2:
The settling time of the Comparator Voltage Reference
must be considered when changing the RA0/AN0/CV
output (see Table 27-4 in Section 27.2).
If CVRR = 0:
CV
where:
= V
= (V
RSRC
RSRC
REF
If CVRR = 1:
CV
where:
DD
REF
CVRSS = 1, CV
CVRSS = 0, CV
Configuring the Comparator
Voltage Reference
REF
/24 step size
/32 step size
CVRSS = 1, CV
CVRSS = 0, CV
R/W-0
U = Unimplemented bit, read as ‘0’
’0’ = Bit is cleared
CVR3
= (CV
– V
CVR3:CVR0
RSRC
+) – (V
SS
= (CVR<3:0>/24) x CV
RSRC
)
REF
REF
REF
x 1/4) + (CVR<3:0>/32) x CV
-)
R/W-0
CVR2
pin
pin
RSRC
RSRC
PIC18FXX8
RSRC
RSRC
15 bits
= (V
= V
= (V
= V
x = Bit is unknown
DD
R/W-0
CVR1
REF
DD
DS41159B-page 251
REF
RSRC
– V
+) – (V
– V
+) – (V
SS
SS
REF
R/W-0
CVR0
REF
-)
RSRC
bit 0
-)
REF