Datasheet

 2012 Microchip Technology Inc. DS30684A-page 45

PIC18(L)F2X/45K50

3.12 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 HFINTOSC

as the clock source and go back to Sleep without

waiting for the primary oscillator to become stable.

When the oscillator module is configured for LP, XT or

HS modes, the Oscillator Start-up Timer (OST) is

enabled (see Section 3.5.1 “Oscillator Start-up Timer

(OST)”). The OST 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 of the OSCCON register is set, program

execution switches to the external oscillator.

3.12.1 TWO-SPEED START-UP MODE

CONFIGURATION

Two-Speed Start-up mode is enabled when all of the

following settings are configured as noted:

• Two-Speed Start-up mode is enabled when the

IESO of the CONFIG1H Configuration register is

set.

• SCS<1:0> (of the OSCCON register) = 00.

• FOSC<2:0> bits of the CONFIG1H Configuration

Two-Speed Start-up mode becomes active after:

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

Power-up Timer (PWRT) has expired, or

• Wake-up from Sleep.

Note: Executing a SLEEP instruction will abort

the oscillator start-up time and will cause

the OSTS bit of the OSCCON register to

remain clear.