PIC16F1516 datasheet(55/344 Pages) MICROCHIP

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Preliminary

DS41452B-page 55

PIC16(L)F1516/7/8/9

5.2.1.4

Secondary Oscillator

The secondary oscillator is a separate crystal oscillator

that is associated with the Timer1 peripheral. It is opti-

mized for timekeeping operations with a 32.768 kHz

crystal connected between the SOSCO and SOSCI

device pins.

The secondary oscillator can be used as an alternate

system clock source and can be selected during

run-time using clock switching. Refer to Section 5.3

“Clock Switching”

for more information.

FIGURE 5-5:

QUARTZ CRYSTAL

OPERATION

(SECONDARY

OSCILLATOR)

5.2.1.5

External RC Mode

The external Resistor-Capacitor (RC) modes support

the use of an external RC circuit. This allows the

designer maximum flexibility in frequency choice while

keeping costs to a minimum when clock accuracy is not

required.

The RC circuit connects to OSC1. OSC2/CLKOUT is

available for general purpose I/O or CLKOUT. The

function of the OSC2/CLKOUT pin is determined by the

state of the CLKOUTEN bit in Configuration Word 1.

Figure 5-6 shows the external RC mode connections.

FIGURE 5-6:

EXTERNAL RC MODES

The RC oscillator frequency is a function of the supply

voltage, the resistor (REXT) and capacitor (CEXT) values

and the operating temperature. Other factors affecting

the oscillator frequency are:

• threshold voltage variation

• component tolerances

• packaging variations in capacitance

The user also needs to take into account variation due

to tolerance of the external RC components used.

Note 1:

Quartz

crystal

characteristics

vary

according

type,

package

and

manufacturer. The user should consult the

manufacturer data sheets for specifications

and recommended application.

Always verify oscillator performance over

the VDD and temperature range that is

expected for the application.

For oscillator design assistance, reference

the following Microchip Applications Notes:

• AN826, “Crystal Oscillator Basics and

Crystal Selection for rfPIC® and PIC®

Devices

” (DS00826)

• AN849, “Basic PIC® Oscillator Design”

(DS00849)

• AN943, “Practical PIC® Oscillator

Analysis and Design

” (DS00943)

• AN949, “Making Your Oscillator Work”

(DS00949)

• TB097, “Interfacing a Micro Crystal

MS1V-T1K 32.768 kHz Tuning Fork

Crystal to a PIC16F690/SS

” (DS91097)

• AN1288, “Design Practices for

Low-Power External Oscillators

”

(DS01288)

32.768 kHz

SOSCI

To Internal

Logic

PIC® MCU

Crystal

SOSCO

Quartz

OSC2/CLKOUT

CEXT

REXT

PIC® MCU

OSC1/CLKIN

FOSC/4 or

Internal

Clock

VDD

VSS

Recommended values: 10 k

  REXT  100 k, <3V

3 k

  REXT  100 k, 3-5V

CEXT > 20 pF, 2-5V

Note

Output depends upon CLKOUTEN bit of the

Configuration Word 1.

I/O(1)

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