PIC16F7X7
14.0
COMPARATOR VOLTAGE
REFERENCE MODULE
supply voltage (also referred to as CV
RSRC
) comes
directly from V
DD
. It should be noted, however, that the
voltage at the top of the ladder is CV
RSRC
– V
SAT
,
where V
SAT
is the saturation voltage of the power
switch transistor. This reference will only be as
accurate as the values of CV
RSRC
and V
SAT
.
The output of the reference generator may be
connected to the RA2/AN2/V
REF
-/CV
REF
pin. This can
be used as a simple D/A function by the user if a very
high-impedance load is used. The primary purpose of
this function is to provide a test path for testing the
reference generator function.
The comparator voltage reference generator is a 16-tap
resistor ladder network that provides a fixed voltage
reference when the comparators are in mode ‘110’. A
programmable register controls the function of the
reference generator. Register 14-1 lists the bit functions
of the CVRCON register.
As shown in Figure 14-1, the resistor ladder is seg-
mented to provide two ranges of CV
REF
values and has
a power-down function to conserve power when the
reference is not being used. The comparator reference
REGISTER 14-1:
CVRCON: COMPARATOR VOLTAGE REFERENCE CONTROL REGISTER
(ADDRESS 9Dh)
R/W-0
CVREN
bit 7
R/W-0
CVROE
R/W-0
CVRR
U-0
—
R/W-0
CVR3
R/W-0
CVR2
R/W-0
CVR1
R/W-0
CVR0
bit 0
bit 7
CVREN:
Comparator Voltage Reference Enable bit
1
= CV
REF
circuit powered on
0
= CV
REF
circuit powered down
CVROE:
Comparator V
REF
Output Enable bit
1
= CV
REF
voltage level is output on RA2/AN2/V
REF
-/CV
REF
pin
0
= CV
REF
voltage level is disconnected from RA2/AN2/V
REF
-/CV
REF
pin
CVRR:
Comparator V
REF
Range Selection bit
1
= 0 to 0.625 CV
RSRC
, with CV
RSRC
/24 step size
0
= 0.25 CV
RSRC
to 0.72 CV
RSRC
, with CV
RSRC
/32 step size
Unimplemented:
Read as ‘0’
CVR3:CVR0:
Comparator V
REF
Value Selection bits 0
≤
CVR3:CVR0
≤
15
When CVRR =
1:
CV
REF
= (CVR<3:0>/24)
•
(CV
RSRC
)
When CVRR =
0:
CV
REF
= 1/4
•
(CV
RSRC
) + (CVR3:CVR0/32)
•
(CV
RSRC
)
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 6
bit 5
bit 4
bit 3-0
2004 Microchip Technology Inc.
DS30498C-page 167
MICROCHIP [ MICROCHIP TECHNOLOGY ]
