PIC16F1503 datasheet(46/340 Pages) MICROCHIP

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PIC16(L)F1503

DS41607A-page 46

Preliminary

 2011 Microchip Technology Inc.

5.2

Clock Source Types

Clock sources can be classified as external or internal.

External clock sources rely on external circuitry for the

clock source to function. Examples are: oscillator mod-

ules (EC mode).

Internal clock sources are contained within the

oscillator module. The oscillator block has two internal

oscillators that are used to generate two system clock

sources:

the

16 MHz

High-Frequency

Internal

Oscillator (HFINTOSC) and the 31 kHz Low-Frequency

Internal Oscillator (LFINTOSC).

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.

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

to switch the system clock source to:

- 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 is connected to the CLKIN input. CLKOUT is

available for general purpose I/O or CLKOUT.

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

EC mode has 3 power modes to select from through

Configuration Words:

• High power, 4-20 MHz (FOSC = 11)

• Medium power, 0.5-4 MHz (FOSC = 10)

• Low power, 0-0.5 MHz (FOSC = 01)

When EC mode is selected, there is no delay in opera-

tion after a Power-on Reset (POR) or wake-up from

Sleep. Because the PIC® MCU design is fully static,

stopping the external clock input will have the effect of

halting the device while leaving all data intact. Upon

restarting the external clock, the device will resume

operation as if no time had elapsed.

FIGURE 5-2:

EXTERNAL CLOCK (EC)

MODE OPERATION

CLKIN

CLKOUT

Clock from

Ext. System

PIC® MCU

FOSC/4 or I/O(1)

Note 1:

Output depends upon CLKOUTEN bit of the

Configuration Words.

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