PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 254

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

PIC18FXX8
FIGURE 22-1:
22.2
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 22-1) keep V
ence source rails. The voltage reference is derived
from the reference source; therefore, the V
changes with fluctuations in that source. The absolute
accuracy of the voltage reference can be found in
Section 27.0.
22.3
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.
DS41159B-page 252
CVREN
or CV
RA0/AN0/CV
Voltage Reference Accuracy/Error
Operation During SLEEP
REF
CVRSS = 0
of Comparator
REF
V
REF
DD
VOLTAGE REFERENCE BLOCK DIAGRAM
V
from approaching the refer-
REF
CVRSS = 1
+
8R
R
REF
output
R
Preliminary
16-to-1 Analog MUX
16 Stages
22.4
A device RESET disables the voltage reference by
clearing bit CVREN (CVRCON register). This RESET
also disconnects the reference from the RA2 pin by
clearing bit CVROE (CVRCON register) and selects
the high voltage range by clearing bit CVRR (CVRCON
register). The CVRSS value select bits, CVRCON<3:0>,
are also cleared.
22.5
The voltage reference module operates independently
of the comparator module. The output of the reference
generator may be connected to the RA0/AN0 pin if the
TRISA<0> bit is set and the CVROE bit (CVRCON<6>)
is set. Enabling the voltage reference output onto the
RA0/AN0 pin, with an input signal present, will increase
current consumption. Connecting RA0/AN0 as a digital
output with CVRSS enabled, will also increase current
consumption.
The RA0/AN0 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 22-2 shows an example buffering technique.
R
Effects of a RESET
Connection Considerations
R
8R
2002 Microchip Technology Inc.
CVR3
CVR0
(From CVRCON<3:0>)
CVRR
RA2/AN2V
CVRSS = 0
CVRSS = 1
REF
REF
-
.