Microchip Technology MA160014 データシート
2010-2012 Microchip Technology Inc.
DS41412E-page 43
PIC18(L)F2X/4XK22
2.12.2
TWO-SPEED START-UP
SEQUENCE
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.
oscillator at the frequency set in the IRCF<2:0>
bits of the OSCCON register.
3.
OST enabled to count 1024 external clock
cycles.
cycles.
4.
OST timed out. External clock is ready.
5.
OSTS is set.
6.
Clock switch finishes according to
2.12.3
CHECKING TWO-SPEED CLOCK
STATUS
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.
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.
FIGURE 2-9:
CLOCK SWITCH TIMING
Old Clock
New Clock
IRCF <2:0>
System Clock
Start-up Time
(1)
Clock Sync
Running
High Speed
Low Speed
Select Old
Select New
New Clk Ready
Low Speed
High Speed
Old Clock
New Clock
IRCF <2:0>
System Clock
Start-up Time
(1)
Clock Sync
Running
Select Old
Select New
New Clk Ready
Note 1: Start-up time includes T
OST
(1024 T
OSC
) for external clocks, plus T
PLL
(approx. 2 ms) for HSPLL mode.