PIC16LC771 datasheet(49/224 Pages) MICROCHIP

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DS41120C-page 49

PIC16C717/770/771

6.2

Timer1 Oscillator

A crystal oscillator circuit is built in between pins T1OSI

(input) and T1OSO (amplifier output). It is enabled by

setting control bit T1OSCEN (T1CON<3>). The oscilla-

tor is a low power oscillator rated up to 200 kHz. It will

continue to run during SLEEP. It is primarily intended

for a 32 kHz crystal. Table 6-1 shows the capacitor

selection for the Timer1 oscillator.

The Timer1 oscillator is identical to the LP oscillator.

The user must provide a software time delay to ensure

proper oscillator start-up.

TABLE 6-1:

CAPACITOR SELECTION FOR

THE TIMER1 OSCILLATOR

6.3

Timer1 Interrupt

The TMR1 Register pair (TMR1H:TMR1L) increments

from 0000h to FFFFh and rolls over to 0000h. The

TMR1 Interrupt, if enabled, is generated on overflow

which is latched in interrupt flag bit TMR1IF (PIR1<0>).

This interrupt can be enabled/disabled by setting/clear-

ing TMR1 interrupt enable bit TMR1IE (PIE1<0>).

6.4

Resetting Timer1 using a CCP

Trigger Output

If the ECCP module is configured in Compare mode to

generate a “special event trigger" (CCP1M<3:0> =

1011

), this signal will reset Timer1 and start an A/D

conversion (if the A/D module is enabled).

Timer1 must be configured for either timer or Synchro-

nized Counter mode to take advantage of this feature.

If Timer1 is running in Asynchronous Counter mode,

this RESET operation may not work.

In the event that a write to Timer1 coincides with a spe-

cial event trigger from ECCP, the write will take prece-

dence.

In this mode of operation, the CCPR1H:CCPR1L regis-

ters pair effectively becomes the period register for

Timer1.

TABLE 6-2:

REGISTERS ASSOCIATED WITH TIMER1 AS A TIMER/COUNTER

Osc Type

Freq

32 kHz

33 pF

100 kHz

15 pF

200 kHz

15 pF

These values are for design guidance only.

Note 1: Higher capacitance increases the stability

of oscillator but also increases the start-up

time.

2: Since each resonator/crystal has its own

characteristics, the user should consult the

resonator/crystal manufacturer for appro-

priate values of external components.

Note:

The special event triggers from the CCP1

module will not set interrupt flag bit

TMR1IF (PIR1<0>).

Address

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Value on:

POR,

BOR

Value on

all other

RESETS

0Bh,8Bh,

10Bh,18Bh

INTCON

GIE

PEIE

T0IE

INTE

RBIE

T0IF

INTF

RBIF

0000 000x

0000 000u

0Ch

PIR1

—

ADIF

—

SSPIF

CCP1IF

TMR2IF

TMR1IF

-0-- 0000

8Ch

PIE1

—

ADIE

—

SSPIE

CCP1IE

TMR2IE

TMR1IE

-0-- 0000

0Eh

TMR1L

Holding register for the Least Significant Byte of the 16-bit TMR1 register

xxxx xxxx

uuuu uuuu

0Fh

TMR1H

Holding register for the Most Significant Byte of the 16-bit TMR1 register

xxxx xxxx

uuuu uuuu

10h

T1CON

—

T1CKPS1

T1CKPS0

T1OSCEN

T1SYNC

TMR1CS

TMR1ON

--00 0000

--uu uuuu

Legend:

x = unknown, u = unchanged, - = unimplemented read as '0'. Shaded cells are not used by the Timer1 module.

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