PIC16F1825T-ESS datasheet(177/448 Pages) MICROCHIP

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DS41440C-page 177

PIC16(L)F1825/1829

19.4

Timer1 Gate Operation

The output resulting from a comparator operation can

be used as a source for gate control of Timer1. See

Section 21.6 “Timer1 Gate”

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

synchronized to Timer1. This ensures that Timer1 does

not increment while a change in the comparator is

occurring.

19.4.1

COMPARATOR OUTPUT

SYNCHRONIZATION

The output from either comparator, C1 or C2, 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 (Figure 19-2) and the Timer1 Block

Diagram (Figure 21-1) for more information.

19.5

Comparator Interrupt

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

• 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

detected while this flag is being cleared, the flag will still

be set at the end of the sequence.

19.6

Comparator Positive Input

Selection

Configuring the CxPCH<1:0> bits of the CMxCON1

analog pin to the non-inverting input of the comparator:

• CxIN+ analog pin

• DAC_output

• FVR (Fixed Voltage Reference)

•VSS (Ground)

See Section 14.0 “Fixed Voltage Reference (FVR)”

for more information on the Fixed Voltage Reference

module.

See Section 17.0 “Digital-to-Analog Converter

(DAC) Module”

for more information on the DAC input

signal.

Any time the comparator is disabled (CxON = 0), all

comparator inputs are disabled.

19.7

Comparator Negative Input

Selection

The CxNCH<1:0> bits of the CMxCON0 register direct

one of four analog pins to the comparator inverting

input.

19.8

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 30.0 “Electrical

Specifications”

for more details.

Note:

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.

Note:

To use CxIN+ and CxINx- pins as analog

input, the appropriate bits must be set in

the ANSEL register and the correspond-

ing TRIS bits must also be set to disable

the output drivers.

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