Microchip Technology DM164130-2 Data Sheet

DS41414D-page 182

 2010-2012 Microchip Technology Inc.

A selectable amount of separation voltage can be
added to the input pins of each comparator to provide a
hysteresis function to the overall operation. Hysteresis
is enabled by setting the CxHYS bit of the CMxCON0
register.
See 

 for

more information.

The output resulting from a comparator operation can
be used as a source for gate control of Timer1. See

 for more information.

This feature is useful for timing the duration or interval
of an analog event.
It is recommended that the comparator output be syn-
chronized to Timer1. This ensures that Timer1 does not
increment while a change in the comparator is occur-
ring.

18.4.1

COMPARATOR OUTPUT 
SYNCHRONIZATION

The output from a comparator can be synchronized
with Timer1 by setting the CxSYNC bit of the
CMxCON0 register.
Once enabled, the comparator output is latched on the
falling edge of the Timer1 source clock. If a prescaler is
used with Timer1, the comparator output is latched after
the prescaling function. To prevent a race condition, the
comparator output is latched on the falling edge of the
Timer1 clock source and Timer1 increments on the
rising edge of its clock source. See the Comparator
Block Diagram (

) and the Timer1 Block

Diagram (

) for more information.

An interrupt can be generated upon a change in the
output value of the comparator for each comparator, a
rising edge detector and a Falling edge detector are
present.
When either edge detector is triggered and its associ-
ated enable bit is set (CxINTP and/or CxINTN bits of
the CMxCON1 register), the Corresponding Interrupt
Flag bit (CxIF bit of the PIR2 register) will be set.
To enable the interrupt, you must set the following bits:
• CxON, CxPOL and CxSP bits of the CMxCON0 

register

• CxIE bit of the PIE2 register
• CxINTP bit of the CMxCON1 register (for a rising 

edge detection)

• CxINTN bit of the CMxCON1 register (for a falling 

edge detection)

• PEIE and GIE bits of the INTCON register
The associated interrupt flag bit, CxIF bit of the PIR2
register, must be cleared in software. If another edge is
detected while this flag is being cleared, the flag will still
be set at the end of the sequence.

Configuring the CxPCH<1:0> bits of the CMxCON1
register directs an internal voltage reference or an
analog pin to the non-inverting input of the comparator:
• CxIN+ analog pin
• DAC output
• FVR (Fixed Voltage Reference)
• V

SS

 (Ground)

See 

for more information on the Fixed Voltage Reference
module.
See 

 for more information on the DAC input

signal.
Any time the comparator is disabled (CxON = 0), all
comparator inputs are disabled.

Although a comparator is disabled, an
interrupt can be generated by changing
the output polarity with the CxPOL bit of
the CMxCON0 register, or by switching
the comparator on or off with the CxON bit
of the CMxCON0 register.