PIC18C658 MICROCHIP [Microchip Technology], PIC18C658 Datasheet - Page 245

• Manufacturer Part Number: PIC18C658
• Description: High-Performance Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

20.2
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 20-1) keep V
ence source rails. The voltage reference is derived
from the reference source; therefore, the V
changes with fluctuations in that source. The tested
absolute accuracy of the voltage reference can be
found in Section 25.0.
20.3
When the device wakes up from SLEEP through an
interrupt or a Watchdog Timer time-out, the contents of
the VRCON register are not affected. To minimize
current consumption in SLEEP mode, the voltage
reference should be disabled.
20.4
A device RESET disables the voltage reference by
clearing bit VREN (VRCON register). This RESET also
disconnects the reference from the RA2 pin by clearing
bit VROE (VRCON register) and selects the high volt-
age range by clearing bit CV
VRSS value select bits, CVRCON<3:0>, are also
cleared.
FIGURE 20-2: VOLTAGE REFERENCE OUTPUT BUFFER EXAMPLE
TABLE 20-1:
Name
VRCON
CMCON
TRISF
2000 Microchip Technology Inc.
Note 1:
Voltage Reference Accuracy/Error
Operation During SLEEP
Effects of a RESET
TRISF7
C2OUT
R is dependent upon the Voltage Reference Configuration VRCON<3:0> and VRCON<5>.
VREN
Bit 7
REGISTERS ASSOCIATED WITH COMPARATOR VOLTAGE REFERENCE
Module
CV
REF
REF
C1OUT
TRISF6 TRISF5 TRISF4 TRISF3 TRISF2
VROE
Bit 6
from approaching the refer-
Impedance
Reference
RR
Voltage
Output
(VRCON register). The
C2INV
R
Bit 5
VRR
(1)
C1INV
VRSS
RF5
Bit 4
Advanced Information
REF
output
•
Bit 3
VR3
CIS
Bit 2
CM2
VR2
20.5
The voltage reference module operates independently
of the comparator module. The output of the reference
generator may be connected to the RF5 pin if the
TRISF<5> bit is set and the VROE bit (VRCON regis-
ter) is set. Enabling the voltage reference output onto
the RF5 pin, with an input signal present, will increase
current consumption. Connecting RF5 as a digital
output with VRSS enabled will also increase current
consumption.
The RF5 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 refer-
ence output for external connections to V
Figure 20-2 shows an example buffering technique.
+
–
TRISF1 TRISF0 1111 1111 1111 1111
Connection Considerations
Bit 1
CM1
VR1
•
Bit 0
CM0
VR0
CV
REF
PIC18CXX8
Output
0000 0000 0000 0000
0000 0000 0000 0000
Value On
POR
DS30475A-page 245
Value On
All Other
RESETS
REF
.