PIC16F7X7 datasheet(83/276 Pages) MICROCHIP

83 / 276 page

 2004 Microchip Technology Inc.

DS30498C-page 81

PIC16F7X7

7.6

Timer1 Oscillator

A crystal oscillator circuit is built between pins T1OSI

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

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

lator is a low-power oscillator, rated up to 32.768 kHz.

It will continue to run during all power-managed modes.

It is primarily intended for a 32 kHz crystal. The circuit

for a typical LP oscillator is shown in Figure 7-3.

Table 7-1 shows the capacitor selection for the Timer1

oscillator.

The user must provide a software time delay to ensure

proper oscillator start-up.

FIGURE 7-3:

EXTERNAL

COMPONENTS FOR THE

TIMER1 LP OSCILLATOR

TABLE 7-1:

CAPACITOR SELECTION FOR

THE TIMER1 OSCILLATOR

7.7

Timer1 Oscillator Layout

Considerations

The Timer1 oscillator circuit draws very little power

during operation. Due to the low-power nature of the

oscillator, it may also be sensitive to rapidly changing

signals in close proximity.

The oscillator circuit, shown in Figure 7-3, should be

located as close as possible to the microcontroller.

There should be no circuits passing within the oscillator

circuit boundaries other than VSS or VDD.

If a high-speed circuit must be located near the oscilla-

tor, a grounded guard ring around the oscillator circuit,

as shown in Figure 7-4, may be helpful when used on

a single sided PCB or in addition to a ground plane.

FIGURE 7-4:

OSCILLATOR CIRCUIT

WITH GROUNDED

GUARD RING

7.8

Resetting Timer1 Using a CCP

Trigger Output

If the CCP1 module is configured in Compare mode to

generate

“special

event

trigger”

signal

(CCP1M3:CCP1M0 = 1011), the 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

special event trigger from CCP1, the write will take

precedence.

In this mode of operation, the CCPR1H:CCPR1L

Timer1.

Osc Type

Freq

32 kHz

33 pF

Note 1: Microchip suggests this value as a starting

point in validating the oscillator circuit.

2: Higher capacitance increases the stability

of the oscillator but also increases the

start-up time.

3: Since each resonator/crystal has its own

characteristics, the user should consult

the resonator/crystal manufacturer for

appropriate

values

external

components.

4: Capacitor values are for design guidance

only.

PIC16F7X7

T1OSI

T1OSO

33 pF

XTAL

32.768 kHz

Note:

See the Notes with Table 7-1 for additional

information about capacitor selection.

Note:

The special event triggers from the CCP1

module will not set interrupt flag bit,

TMR1IF (PIR1<0>).

OSC1

VSS

OSC2

RC0

RC1

RC2

PIC16F7X7 Datasheet(PDF) 83 Page - Microchip Technology

PIC16F7X7 Datasheet(HTML) 83 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL