PIC18LF2X_13 Datasheet, PDF (43/560 Pages) Microchip Technology – PIC18(L)F2X/45K50 USB Flash MCU Product Brief

PIC18(L)F2X/4XK22
2.12.2 TWO-SPEED START-UP
SEQUENCE
1. Wake-up from Power-on Reset or Sleep.
2. Instructions begin executing by the internal
oscillator at the frequency set in the IRCF<2:0>
bits of the OSCCON register.
3. OST enabled to count 1024 external clock
cycles.
4. OST timed out. External clock is ready.
5. OSTS is set.
6. Clock switch finishes according to Figure 2-9
FIGURE 2-9:
CLOCK SWITCH TIMING
High Speed Low Speed
2.12.3 CHECKING TWO-SPEED CLOCK
STATUS
Checking the state of the OSTS bit of the OSCCON
register will confirm if the microcontroller is running
from the external clock source, as defined by the
FOSC<2:0> bits in CONFIG1H Configuration register,
or the internal oscillator. OSTS = 0 when the external
oscillator is not ready, which indicates that the system
is running from the internal oscillator.
Old Clock
Start-up Time⁽¹⁾
New Clock
New Clk Ready
IRCF <2:0> Select Old
Select New
System Clock
Clock Sync
Running
Low Speed High Speed
Old Clock
Start-up Time⁽¹⁾
New Clock
New Clk Ready
IRCF <2:0> Select Old
Select New
System Clock
Clock Sync
Running
Note 1: Start-up time includes TOST (1024 TOSC) for external clocks, plus TPLL (approx. 2 ms) for HSPLL mode.
 2010-2012 Microchip Technology Inc.
DS41412E-page 43