PIC16F882/883/884/886/887
8.2
Comparator Control
Note 1: The CxOE bit overrides the PORT data
latch. Setting the CxON has no impact on
the port override.
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.
2: The internal output of the comparator is
latched with each instruction cycle.
Unless otherwise specified, external
outputs are not latched.
The CM1CON0 and CM2CON0 registers (see Registers
8-1 and 8-2, respectively) contain the control and Status
bits for the following:
8.2.5
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.
• Enable
• Input selection
• Reference selection
• Output selection
• Output polarity
Table 8-1 shows the output state versus input
conditions, including polarity control.
8.2.1
COMPARATOR ENABLE
TABLE 8-1:
COMPARATOR OUTPUT
STATE VS. INPUT
CONDITIONS
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.
Input Condition
CxPOL
CxOUT
CxVIN- > CxVIN+
CxVIN- < CxVIN+
CxVIN- > CxVIN+
CxVIN- < CxVIN+
0
0
1
1
0
1
1
0
8.2.2
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 CxIN- pins as analog
inputs, the appropriate bits must be set in
the ANSEL and ANSELH registers and the
corresponding TRIS bits must also be set
to disable the output drivers.
8.3
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 17.0
“Electrical Specifications” for more details.
8.2.3
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 8.10 “Comparator Voltage Reference” for
more information on the internal Voltage Reference
module.
8.2.4
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
© 2007 Microchip Technology Inc.
Preliminary
DS41291D-page 85
MICROCHIP [ MICROCHIP ]
