PIC18F23K22 Datasheet, PDF (41/492 Pages) Microchip Technology – 28/40/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology

PIC18(L)F2X/4XK22
TABLE 2-3: OSC1 AND OSC2 PIN STATES IN SLEEP MODE
OSC Mode
OSC1 Pin
OSC2 Pin
RC, INTOSC with CLKOUT Floating, external resistor should pull high
RC with IO
Floating, external resistor should pull high
INTOSC with IO
Configured as PORTA, bit 7
EC with IO
Floating, pulled by external clock
EC with CLKOUT
Floating, pulled by external clock
LP, XT, HS
Feedback inverter disabled at quiescent
voltage level
At logic low (clock/4 output)
Configured as PORTA, bit 6
Configured as PORTA, bit 6
Configured as PORTA, bit 6
At logic low (clock/4 output)
Feedback inverter disabled at quiescent
voltage level
Note: See Table 4-2 in Section 4.0 “Reset” for time-outs due to Sleep and MCLR Reset.
2.9 Clock Switching
The system clock source can be switched between
external and internal clock sources via software using
the System Clock Select (SCS<1:0>) bits of the
OSCCON register.
PIC18(L)F2X/4XK22 devices contain circuitry to pre-
vent clock “glitches” when switching between clock
sources. A short pause in the device clock occurs dur-
ing the clock switch. The length of this pause is the sum
of two cycles of the old clock source and three to four
cycles of the new clock source. This formula assumes
that the new clock source is stable.
Clock transitions are discussed in greater detail in
Section 3.1.2 “Entering Power-Managed Modes”.
2.9.1
SYSTEM CLOCK SELECT
(SCS<1:0>) BITS
The System Clock Select (SCS<1:0>) bits of the
OSCCON register select the system clock source that
is used for the CPU and peripherals.
• When SCS<1:0> = 00, the system clock source is
determined by configuration of the FOSC<3:0>
bits in the CONFIG1H Configuration register.
• When SCS<1:0> = 10, the system clock source is
chosen by the internal oscillator frequency
selected by the INTSRC bit of the OSCTUNE
register, the MFIOSEL bit of the OSCCON2
register and the IRCF<2:0> bits of the OSCCON
register.
• When SCS<1:0> = 01, the system clock source is
the 32.768 kHz secondary oscillator shared with
Timer1, Timer3 and Timer5.
After a Reset, the SCS<1:0> bits of the OSCCON
register are always cleared.
Note:
Any automatic clock switch, which may
occur from Two-Speed Start-up or Fail-Safe
Clock Monitor, does not update the
SCS<1:0> bits of the OSCCON register.
The user can monitor the SOSCRUN,
MFIOFS and LFIOFS bits of the
OSCCON2 register, and the HFIOFS and
OSTS bits of the OSCCON register to
determine the current system clock source.
2.9.2
OSCILLATOR START-UP TIME-OUT
STATUS (OSTS) BIT
The Oscillator Start-up Time-out Status (OSTS) bit of
the OSCCON register indicates whether the system
clock is running from the external clock source, as
defined by the FOSC<3:0> bits in the CONFIG1H
Configuration register, or from the internal clock
source. In particular, when the primary oscillator is the
source of the primary clock, OSTS indicates that the
Oscillator Start-up Timer (OST) has timed out for LP,
XT or HS modes.
 2010 Microchip Technology Inc.
Preliminary
DS41412B-page 41