PIC16F631 datasheet(103/294 Pages) MICROCHIP

103 / 294 page

DS41262D-page 101

PIC16F631/677/685/687/689/690

8.8

Additional Comparator Features

There are three additional comparator features:

• Timer1 count enable (gate)

• Synchronizing output with Timer1

• Simultaneous read of comparator outputs

8.8.1

COMPARATOR C2 GATING TIMER1

This feature can be used to time the duration or interval

of analog events. Clearing the T1GSS bit of the

CM2CON1 register will enable Timer1 to increment

based on the output of Comparator C2. This requires

that Timer1 is on and gating is enabled. See

Section 6.0 “Timer1 Module with Gate Control” for

details.

It is recommended to synchronize the comparator with

Timer1 by setting the C2SYNC bit when the comparator

is used as the Timer1 gate source. This ensures Timer1

does not miss an increment if the comparator changes

during an increment.

8.8.2

SYNCHRONIZING COMPARATOR

C2 OUTPUT TO TIMER1

The Comparator C2 output can be synchronized with

Timer1 by setting the C2SYNC bit of the CM2CON1

falling edge of the Timer1 clock source. 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 8-3) and the Timer1 Block

Diagram (Figure 6-1) for more information.

8.8.3

SIMULTANEOUS COMPARATOR

OUTPUT READ

The MC1OUT and MC2OUT bits of the CM2CON1

The ability to read both outputs simultaneously from a

single register eliminates the timing skew of reading

separate registers.

Note 1: Obtaining the status of C1OUT or C2OUT

by reading CM2CON1 does not affect the

comparator interrupt mismatch registers.

CM2CON1: COMPARATOR C2 CONTROL REGISTER 1

R-0

U-0

R/W-1

R/W-0

MC1OUT

MC2OUT

—

T1GSS

C2SYNC

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7

MC1OUT: Mirror Copy of C1OUT bit

bit 6

MC2OUT: Mirror Copy of C2OUT bit

bit 5-2

Unimplemented: Read as ‘0’

bit 1

T1GSS: Timer1 Gate Source Select bit(1)

= Timer1 gate source is T1G

= Timer1 gate source is SYNCC2OUT.

bit 0

C2SYNC: Comparator C2 Output Synchronization bit(2)

= Output is synchronous to falling edge of Timer1 clock

= Output is asynchronous

Note 1:

Refer to Section 6.6 “Timer1 Gate”.

Refer to Figure 8-3.

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