PIC18F-LF1XK50 Datasheet, PDF (226/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

PIC18F/LF1XK50
18.2 Comparator Control
Each comparator has a separate control and
Configuration register: CM1CON0 for Comparator C1
and CM2CON0 for Comparator C2. In addition,
Comparator C2 has a second control register,
CM2CON1, for controlling the interaction with Timer1 and
simultaneous reading of both comparator outputs.
The CM1CON0 and CM2CON0 registers (see Registers
18-1 and 18-2, respectively) contain the control and
status bits for the following:
• Enable
• Input selection
• Reference selection
• Output selection
• Output polarity
• Speed selection
18.2.1 COMPARATOR ENABLE
Setting the CxON bit of the CMxCON0 register enables
the comparator for operation. Clearing the CxON bit
disables the comparator resulting in minimum current
consumption.
18.2.2 COMPARATOR INPUT SELECTION
The CxCH<1:0> bits of the CMxCON0 register direct
one of four analog input pins to the comparator
inverting input.
Note:
To use CxIN+ and C12INx- pins as analog
inputs, the appropriate bits must be set in
the ANSEL register and the
corresponding TRIS bits must also be set
to disable the output drivers.
18.2.3 COMPARATOR REFERENCE
SELECTION
Setting the CxR bit of the CMxCON0 register directs an
internal voltage reference or an analog input pin to the
non-inverting input of the comparator. See
Section 21.0 “VOLTAGE REFERENCES” for more
information on the Internal Voltage Reference module.
18.2.4 COMPARATOR OUTPUT
SELECTION
The output of the comparator can be monitored by
reading either the CxOUT bit of the CMxCON0 register
or the MCxOUT bit of the CM2CON1 register. In order
to make the output available for an external connection,
the following conditions must be true:
• CxOE bit of the CMxCON0 register must be set
• Corresponding TRIS bit must be cleared
• CxON bit of the CMxCON0 register must be set
Both comparators share the same output pin
(C12OUT). Priority is determined by the states of the
C1OE and C2OE bits.
TABLE 18-1:
C10E
0
0
1
1
COMPARATOR OUTPUT
PRIORITY
C2OE
C12OUT
0
I/O
1
C2OUT
0
C1OUT
1
C2OUT
Note 1: The CxOE bit overrides the PORT data
latch. Setting the CxON has no impact on
the port override.
2: The internal output of the comparator is
latched with each instruction cycle.
Unless otherwise specified, external
outputs are not latched.
18.2.5 COMPARATOR OUTPUT POLARITY
Inverting the output of the comparator is functionally
equivalent to swapping the comparator inputs. The
polarity of the comparator output can be inverted by
setting the CxPOL bit of the CMxCON0 register.
Clearing the CxPOL bit results in a non-inverted output.
Table 18-2 shows the output state versus input
conditions, including polarity control.
TABLE 18-2: COMPARATOR OUTPUT
STATE VS. INPUT
CONDITIONS
Input Condition CxPOL
CxOUT
CxVIN- > CxVIN+
0
0
CxVIN- < CxVIN+
0
1
CxVIN- > CxVIN+
1
1
CxVIN- < CxVIN+
1
0
18.2.6 COMPARATOR SPEED SELECTION
The trade-off between speed or power can be opti-
mized during program execution with the CxSP control
bit. The default state for this bit is ‘1’ which selects the
normal speed mode. Device power consumption can
be optimized at the cost of slower comparator propaga-
tion delay by clearing the CxSP bit to ‘0’.
18.3 Comparator Response Time
The comparator output is indeterminate for a period of
time after the change of an input source or the selection
of a new reference voltage. This period is referred to as
the response time. The response time of the
comparator differs from the settling time of the voltage
reference. Therefore, both of these times must be
considered when determining the total response time
to a comparator input change. See the Comparator and
Voltage Reference Specifications in Section 27.0
“Electrical Specifications” for more details.
DS41350E-page 226
Preliminary
 2010 Microchip Technology Inc.