PIC18F2420 MICROCHIP [Microchip Technology], PIC18F2420 Datasheet - Page 242

• Manufacturer Part Number: PIC18F2420
• Description: 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F2420/2520/4420/4520
FIGURE 21-1:
21.2
The full range of voltage reference cannot be realized
due to the construction of the module. The transistors
on the top and bottom of the resistor ladder network
(Figure 21-1) keep CV
ence source rails. The voltage reference is derived
from the reference source; therefore, the CV
changes with fluctuations in that source. The tested
absolute accuracy of the voltage reference can be
found in Section 26.0 “Electrical Characteristics”.
21.3
When the device wakes up from Sleep through an
interrupt or a Watchdog Timer time-out, the contents of
the CVRCON register are not affected. To minimize
current consumption in Sleep mode, the voltage
reference should be disabled.
DS39631A-page 240
Voltage Reference Accuracy/Error
Operation During Sleep
CVRR
V
V
CVREN
V
REF
DD
REF
REF
VOLTAGE REFERENCE BLOCK DIAGRAM
+
-
from approaching the refer-
CVRSS = 0
CVRSS = 1
CVRSS = 1
CVRSS = 0
16 Steps
REF
output
Preliminary
8R
R
R
R
R
R
R
R
clearing bit, CVREN (CVRCON<7>). This Reset also
disconnects the reference from the RA2 pin by clearing
21.4
A device Reset disables the voltage reference by
bit, CVROE (CVRCON<6>) and selects the high-voltage
range by clearing bit, CVRR (CVRCON<5>). The CVR
value select bits are also cleared.
21.5
The voltage reference module operates independently
of the comparator module. The output of the reference
generator may be connected to the RA2 pin if the
CVROE bit is set. Enabling the voltage reference out-
put onto RA2 when it is configured as a digital input will
increase current consumption. Connecting RA2 as a
digital output with CVRSS enabled will also increase
current consumption.
The RA2 pin can be used as a simple D/A output with
limited drive capability. Due to the limited current drive
capability, a buffer must be used on the voltage
reference output for external connections to V
Figure 21-2 shows an example buffering technique.
8R
Effects of a Reset
Connection Considerations
CVR3:CVR0
 2004 Microchip Technology Inc.
CV
REF
REF
.