PIC16F1507-ESLASHSS. datasheet(44/278 Pages) MICROCHIP

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PIC16(L)F1507

DS40001586D-page 44

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5.2

Clock Source Types

Clock sources can be classified as external, internal or

peripheral.

External clock sources rely on external circuitry for the

clock source to function. Examples are: oscillator mod-

ules (ECH, ECM, ECL modes).

Internal clock sources are contained within the oscillator

module. The internal oscillator block has two internal

oscillators that are used to generate the internal system

clock sources: the 16 MHz High-Frequency Internal

Oscillator (HFINTOSC) and the 31 kHz Low-Frequency

Internal Oscillator (LFINTOSC).

The peripheral clock source is a nominal 600 kHz

internal RC oscillator, FRC. The FRC is traditionally

used with the ADC module, but is sometimes available

to other peripherals. See Section 5.2.2.4 “Peripheral

Clock Sources”

The system clock can be selected between external or

internal clock sources via the System Clock Select

(SCS) bits in the OSCCON register. See Section

5.3 “Clock Switching”

for additional information.

5.2.1

EXTERNAL CLOCK SOURCES

An external clock source can be used as the device

system clock by performing one of the following

actions:

• Program the FOSC<1:0> bits in the Configuration

Words to select an external clock source that 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:

- Secondary oscillator during run-time, or

- An external clock source determined by the

value of the FOSC bits.

See Section 5.3 “Clock Switching” for more informa-

tion.

5.2.1.1

EC Mode

The External Clock (EC) mode allows an externally

generated logic level signal to be the system clock

source. When operating in this mode, an external clock

source

connected

the

OSC1

input.

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

CLKOUT. Figure 5-2 shows the pin connections for EC

mode.

EC mode has three power modes to select from through

the FOSC bits in the Configuration Words:

• ECH – High power, 4-20 MHz

• ECM – Medium power, 0.5-4 MHz

• ECL – Low power, 0-0.5 MHz

FIGURE 5-2:

EXTERNAL CLOCK (EC)

MODE OPERATION

Clock from

Ext. system

FOSC/4 or I/O

(1)

OSC1/CLKIN

PIC

® MCU

OSC2/CLKOUT

Note 1:

Output depends upon the CLKOUTEN bit

of the Configuration Words.

Rev. 10-000045A

7/30/2013

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