PIC16F1459-ESSQTP datasheet(62/418 Pages) MICROCHIP

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PIC16(L)F1454/5/9

DS41639A-page 62

Preliminary

 2012 Microchip Technology Inc.

5.2.1.6

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

CLKOUTEN bit in Configuration Words.

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.

5.2.2

INTERNAL CLOCK SOURCES

The device may be configured to use the internal oscil-

lator block as the system clock by performing one of the

following actions:

• Program the FOSC<2:0> bits in Configuration

Words to select the INTOSC clock source, which

will be used as the default system clock upon a

device Reset.

• Write the SCS<1:0> bits in the OSCCON register

to switch the system clock source to the internal

oscillator during run-time. See Section 5.3 “CPU

Clock Divider”for more information.

In INTOSC mode, OSC1/CLKIN is available for general

purpose I/O. OSC2/CLKOUT is available for general

purpose I/O or CLKOUT.

The function of the OSC2/CLKOUT pin is determined

by the CLKOUTEN bit in Configuration Words.

The internal oscillator block has two independent

oscillators that provides the internal system clock

source.

The

HFINTOSC

(High-Frequency

Internal

Oscillator) is factory calibrated and operates at

16 MHz. The frequency of the HFINTOSC can be

user-adjusted via software using the OSCTUNE

The

LFINTOSC

(Low-Frequency

Internal

Oscillator) is uncalibrated and operates at

31 kHz.

5.2.2.1

HFINTOSC

The High-Frequency Internal Oscillator (HFINTOSC) is

a factory calibrated 16 MHz internal clock source. The

frequency of the HFINTOSC can be altered via

software using the OSCTUNE register (Register 5-3).

The output of the HFINTOSC connects to a postscaler

and multiplexer (see Figure 5-1). The frequency derived

from the HFINTOSC can be selected via software using

the IRCF<3:0> bits of the OSCCON register. See

Section 5.2.2.4

“Internal

Oscillator

Frequency

Selection” for more information.

The HFINTOSC is enabled by:

• Configure the IRCF<3:0> bits of the OSCCON

•FOSC<2:0> = 100, or

• Set the System Clock Source (SCS) bits of the

OSCCON register to ‘1x’.

A fast start-up oscillator allows internal circuits to

power-up and stabilize before switching to HFINTOSC.

The High-Frequency Internal Oscillator Ready bit

(HFIOFR) of the OSCSTAT register indicates when the

HFINTOSC is running.

The High-Frequency Internal Oscillator Stable bit

(HFIOFS) of the OSCSTAT register indicates when the

HFINTOSC is running within 0.5% of its final value.

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 1:

Output depends upon CLKOUTEN bit of the

Configuration Words.

I/O(1)

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