PIC16F917ESLASHML301 datasheet(80/272 Pages) MICROCHIP

80 / 272 page

PIC16F917/916/914/913

DS41250E-page 78

Preliminary

4.5.2

OSCILLATOR START-UP TIME-OUT

STATUS BIT

The Oscillator Start-up Time-out Status (OSTS) bit

(OSCCON<3>) indicates whether the system clock is

running from the external clock source, as defined by

the FOSC bits, or from the internal clock source. In

particular, OSTS indicates that the Oscillator Start-up

Timer (OST) has timed out for LP, XT or HS modes.

4.6

Two-Speed Clock Start-up Mode

Two-Speed Start-up mode provides additional power

savings by minimizing the latency between external

oscillator start-up and code execution. In applications

that make heavy use of the Sleep mode, Two-Speed

Start-up will remove the external oscillator start-up

time from the time spent awake and can reduce the

overall power consumption of the device.

This mode allows the application to wake-up from

Sleep, perform a few instructions using the INTOSC

as the clock source and go back to Sleep without

waiting for the primary oscillator to become stable.

When the PIC16F917/916/914/913 is configured for

LP, XT or HS modes, the Oscillator Start-up Timer

(OST) is enabled (see Section 4.3.1 “Oscillator

Start-up Timer (OST)”). The OST timer will suspend

program execution until 1024 oscillations are counted.

Two-Speed Start-up mode minimizes the delay in code

execution by operating from the internal oscillator as

the OST is counting. When the OST count reaches

1024 and the OSTS bit (OSCCON<3>) is set, program

execution switches to the external oscillator.

4.6.1

TWO-SPEED START-UP MODE

CONFIGURATION

Two-Speed Start-up mode is configured by the

following settings:

• IESO = 1 (CONFIG<10>) Internal/External

Switchover bit.

•SCS = 0.

• FOSC configured for LP, XT or HS mode.

Two-Speed Start-up mode is entered after:

• Power-on Reset (POR) and, if enabled, after

PWRT has expired, or

• Wake-up from Sleep.

If the external clock oscillator is configured to be anything

other than LP, XT or HS mode, then Two-Speed Start-up

is disabled. This is because the external clock oscillator

does not require any stabilization time after POR or an

exit from Sleep.

4.6.2

TWO-SPEED START-UP

SEQUENCE

Wake-up from Power-on Reset or Sleep.

Instructions begin execution by the internal

oscillator at the frequency set in the IRCF bits

(OSCCON<6:4>).

OST enabled to count 1024 clock cycles.

OST timed out, wait for falling edge of the

internal oscillator.

OSTS is set.

System clock held low until the next falling edge

of new clock (LP, XT or HS mode).

System clock is switched to external clock

source.

4.6.3

CHECKING EXTERNAL/INTERNAL

CLOCK STATUS

Checking the state of the OSTS bit (OSCCON<3>) will

confirm if the PIC16F917/916/914/913 is running from

the external clock source as defined by the FOSC bits

in the Configuration Word (CONFIG) or the internal

oscillator.

Note:

Executing a SLEEP instruction will abort

the oscillator start-up time and will cause

the OSTS bit (OSCCON<3>) to remain

clear.

PIC16F917E/ML301 Datasheet(PDF) 80 Page - Microchip Technology

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