PIC12F683
3.5.2
OSCILLATOR START-UP TIME-OUT
STATUS BIT
3.6.1
TWO-SPEED START-UP MODE
CONFIGURATION
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 internal clock source. In partic-
ular, OSTS indicates that the Oscillator Start-up Timer
(OST) has timed out for LP, XT or HS modes.
Two-Speed Start-up mode is configured by the
following settings:
• IESO = 1(CONFIG<10>) Internal/External Switch
Over bit.
• SCS = 0.
• FOSC configured for LP, XT or HS mode.
Two-Speed Start-up mode is entered after:
3.6
Two-Speed Clock Start-up Mode
• Power-on Reset (POR) and, if enabled, after
PWRT has expired, or
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.
• Wake-up from Sleep.
If the external clock oscillator is configured to be any-
thing 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.
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.
3.6.2
TWO-SPEED START-UP
SEQUENCE
1. Wake-up from Power-on Reset or Sleep.
Note:
Executing a SLEEP instruction will abort
the oscillator start-up time and will cause
the OSTS bit (OSCCON<3>) to remain
clear.
2. Instructions begin execution by the internal
oscillator at the frequency set in the IRCF bits
(OSCCON<6:4>).
3. OST enabled to count 1024 clock cycles.
When the PIC12F683 is configured for LP, XT or HS
modes, the Oscillator Start-up Timer (OST) is enabled
(see Section 3.3.1 “Oscillator Start-up Timer
(OST)”). The OST timer will suspend program execu-
tion 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. OST timed out, wait for falling edge of the
internal oscillator.
5. OSTS is set.
6. System clock held low until the next falling edge
of new clock (LP, XT or HS mode).
7. System clock is switched to external clock
source.
2004 Microchip Technology Inc.
Preliminary
DS41211B-page 25
MICROCHIP [ MICROCHIP ]
