PIC18F44J50-I Datasheet, PDF (393/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

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24.2 Voltage Reference Accuracy/Error
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
(see Figure 24-1) keep CVREF from approaching the
reference source rails. The voltage reference is derived
from the reference source; therefore, the CVREF output
changes with fluctuations in that source. The accuracy
of the voltage reference can be found in Section 30.0
“Electrical Characteristics”.
24.3 Connection Considerations
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.
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 VREF. See
Figure 24-2 for an example buffering technique.
24.4 Operation During Sleep
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.
24.5 Effects of a Reset
A device Reset disables the voltage reference by
clearing bit, CVREN (CVRCON<7>). This Reset also
disconnects the reference from the RA2 pin by clearing
bit, CVROE (CVRCON<6>) and selects the high-voltage
range by clearing bit, CVRR (CVRCON<5>). The CVR
value select bits are also cleared.
FIGURE 24-2:
COMPARATOR VOLTAGE REFERENCE OUTPUT BUFFER EXAMPLE
PIC18F46J50
CVREF
Module
R⁽¹⁾
Voltage
Reference
Output
Impedance
RA2
+
–
CVREF Output
Note 1: R is dependent upon the Comparator Voltage Reference Configuration bits, CVRCON<5> and CVRCON<3:0>.
TABLE 24-1: REGISTERS ASSOCIATED WITH COMPARATOR VOLTAGE REFERENCE
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Reset
Values
on Page:
CVRCON CVREN CVROE CVRR
r
CVR3 CVR2 CVR1 CVR0
74
CM1CON
CON
COE
CPOL EVPOL1 EVPOL0 CREF
CCH1 CCH0
70
CM2CON
CON
COE
CPOL EVPOL1 EVPOL0 CREF
CCH1 CCH0
70
TRISA
TRISA7 TRISA6 TRISA5
—
TRISA3 TRISA2 TRISA1 TRISA0
72
ANCON0 PCFG7⁽¹⁾ PCFG6⁽¹⁾ PCFG5⁽¹⁾ PCFG4 PCFG3 PCFG2 PCFG1 PCFG0
74
ANCON1
VBGEN
r
—
PCFG12 PCFG11 PCFG10 PCFG9 PCFG8
74
Legend: — = unimplemented, read as ‘0’, r = reserved. Shaded cells are not used with the comparator voltage
reference.
Note 1: These bits are only available on 44-pin devices.
 2011 Microchip Technology Inc.
DS39931D-page 393