PIC16F1503 datasheet(48/340 Pages) MICROCHIP

48 / 340 page

PIC16(L)F1503

DS41607A-page 48

Preliminary

 2011 Microchip Technology Inc.

5.2.2.3

Internal Oscillator Frequency

Selection

The system clock speed can be selected via software

using the Internal Oscillator Frequency Select bits

IRCF<3:0> of the OSCCON register.

The outputs of the 16 MHz HFINTOSC postscaler and

the LFINTOSC connect to a multiplexer (see

Figure 5-1). The Internal Oscillator Frequency Select

bits IRCF<3:0> of the OSCCON register select the

frequency output of the internal oscillators. One of the

following frequencies can be selected via software:

•HFINTOSC

-16 MHz

-8 MHz

-4 MHz

-2 MHz

-1 MHz

- 500 kHz (default after Reset)

- 250 kHz

- 125 kHz

- 62.5 kHz

- 31.25 kHz

•LFINTOSC

-31 kHz

The IRCF<3:0> bits of the OSCCON register allow

duplicate selections for some frequencies. These dupli-

cate choices can offer system design trade-offs. Lower

power consumption can be obtained when changing

oscillator sources for a given frequency. Faster transi-

tion times can be obtained between frequency changes

that use the same oscillator source.

5.2.2.4

Internal Oscillator Clock Switch

Timing

When switching between the HFINTOSC and the

LFINTOSC, the new oscillator may already be shut

down to save power (see Figure 5-3). If this is the case,

there is a delay after the IRCF<3:0> bits of the

OSCCON register are modified before the frequency

selection takes place. The OSCSTAT register will

reflect the current active status of the HFINTOSC and

LFINTOSC oscillators. The sequence of a frequency

selection is as follows:

IRCF<3:0> bits of the OSCCON register are

modified.

If the new clock is shut down, a clock start-up

delay is started.

Clock switch circuitry waits for a falling edge of

the current clock.

Clock switch is complete.

See Figure 5-3 for more details.

If the internal oscillator speed is switched between two

clocks of the same source, there is no start-up delay

before the new frequency is selected.

Start-up delay specifications are located in the

oscillator

tables

Section 28.0

“Electrical

Specifications”.

Note:

Following any Reset, the IRCF<3:0> bits

of the OSCCON register are set to ‘0111’

and the frequency selection is set to

500 kHz. The user can modify the IRCF

bits to select a different frequency.

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