
2007 Microchip Technology Inc.
Preliminary
DS41268C-page 49
PIC12F510/16F506
8.0
COMPARATOR VOLTAGE
REFERENCE MODULE
(PIC16F506 ONLY)
The Comparator Voltage Reference module also
allows the selection of an internally generated voltage
reference for one of the C2 comparator inputs. The
VRCON register (Register 8-1) controls the Voltage
Reference module shown in Figure 8-1.
8.1
Configuring The Voltage
Reference
The voltage reference can output 32 voltage levels; 16
in a high range and 16 in a low range.
Equation 8-1 determines the output voltages:
EQUATION 8-1:
8.2
Voltage Reference Accuracy/Error
The full range of V
SS
to V
DD
cannot be realized due to
construction of the module. The transistors on the top
and bottom of the resistor ladder network (Figure 8-1)
keep CV
REF
from approaching V
SS
or V
DD
. The excep-
tion is when the module is disabled by clearing the
VREN bit (VRCON<7>). When disabled, the reference
voltage is V
SS
when VR<3:0> is ‘
0000
’ and the VRR
(VRCON<5>) bit is set. This allows the comparator to
detect a zero-crossing and not consume the CV
REF
module current.
The voltage reference is V
DD
derived and, therefore,
the CV
REF
output changes with fluctuations in V
DD
. The
tested absolute accuracy of the comparator voltage ref-
erence can be found in
Section 13.2 “DC Character-
istics: PIC12F510/16F506 (Extended)”
.
REGISTER 8-1:
VRR = 1 (low range): CV
REF
= (VR<3:0>/24) x V
DD
VRR = 0 (high range):
CV
REF
= (V
DD
/4) + (VR<3:0> x V
DD
/32)
VRCON: VOLTAGE REFERENCE CONTROL REGISTER (PIC16F506 ONLY)
R/W-0
VREN
R/W-0
VROE
R/W-1
VRR
U-0
—
R/W-1
VR3
R/W-1
VR2
R/W-1
VR1
R/W-1
VR0
bit 7
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
bit 7
VREN:
CV
REF
Enable bit
1
= CV
REF
is powered on
0
= CV
REF
is powered down, no current is drawn
VROE:
CV
REF
Output Enable bit
(1)
1
= CV
REF
output is enabled
0
= CV
REF
output is disabled
VRR:
CV
REF
Range Selection bit
1
= Low range
0
= High range
Unimplemented:
Read as ‘
0
’
VR<3:0>
CV
REF
Value Selection bit
When V
RR
=
1
: CV
REF
= (VR<3:0>/24)*V
DD
When V
RR
=
0
: CV
REF
= V
DD
/4+(VR<3:0>/32)*V
DD
bit 6
bit 5
bit 4
bit 3-0
Note 1:
When this bit is set, the TRIS for the CV
REF
pin is overridden and the analog voltage is placed on the
CV
REF
pin.
2:
CV
REF
controls for ratio metric reference applies to Comparator 2 on the PIC12F506 only.