2001 Microchip Technology Inc.
Preliminary
DS41171A-page 61
PIC16C781/782
7.0
VOLTAGE REFERENCE
MODULE (VR)
The Voltage Reference module provides an on-chip
nominal 3.072V reference voltage for the following:
ADC converter
DAC converter
VR output on the RB0/INT/AN4/VR pin
The source for the reference voltage comes from a
bandgap reference.
The control register for this module is the REFCON
register shown in Register 7-1.
Setting the VREN flag (REFCON<3>), enables the
module. Following initial start-up, the module should be
for information concerning stabilization times and
conditions.
To route the reference voltage to the external RB0/INT/
AN4/VR pin, the VROE flag (REFCON<2>) must be
set.
7.1
Effects of RESET
A device RESET clears the REFCON register, dis-
abling the voltage reference.
7.2
Registers Associated with VR
A summary of the registers associated with VR is
REGISTER 7-1:
VOLTAGE REFERENCE CONTROL REGISTER (REFCON: 9Bh)
TABLE 7-1:
SUMMARY OF REGISTERS ASSOCIATED WITH VR
Note 1: If the VR module is to be used by the
DAC, ADC, or VR output:, the VR module
must
be
enabled
using
VREN
(REFCON<3>).
2: When VREN = 1 and VROE = 1, the out-
put driver for RB0/INT/AN4/VR will be
driven tri-state and the analog driver for
the VR output will be enabled. A read of
RB0 will return a ‘0’.
U-0
R/W-0
U-0
—
VREN
VROE
—
bit 7
bit 0
bit 7-4
Unimplemented: Read as ‘0’
bit 3
VREN: Voltage Reference Enable bit (VR = 3.072V nominal)
1
= VR reference is enabled
0
= VR reference is disabled
bit 2
VROE: Voltage Reference Output Enable bit
If VREN = 1:
1
= Enabled, VR voltage reference is output on RB0
0
= Voltage reference is not available externally
If VREN = 0:
This bit is ignored
bit 1-0
Unimplemented: Read as ‘0’
Legend:
R = Readable bit
W = Writable bit
U = Unimplemented bit, read as ‘0’
- n = Value at POR
’1’ = Bit is set
’0’ = Bit is cleared
x = Bit is unknown
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on:
POR,
BOR
Value on
all other
RESETS
09Bh
REFCON
—
VREN
VROE
—
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