Datasheet

PIC18F47J13 FAMILY
DS39974A-page 42 Preliminary  2010 Microchip Technology Inc.
The use of the flag and control bits in the OSCCON
register is discussed in more detail in Section 4.0
“Low-Power Modes”.
3.3.2 OSCILLATOR TRANSITIONS
PIC18F47J13 family devices contain circuitry to
prevent 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 more detail in
Section 4.1.2 “Entering Power-Managed Modes”.
Note 1: The Timer1 crystal driver is enabled by
setting the T1OSCEN bit in the Timer1
Control register (T1CON<3>). If the
Timer1 oscillator is not enabled, then any
attempt to select the Timer1 clock source
will be ignored, unless the CONFIG2L
register’s SOSCSEL<1:0> bits are set to
Digital mode.
2: If Timer1 is driving a crystal, it is recom-
mended that the Timer1 oscillator be
operating and stable prior to switching to
it as the clock source; otherwise, a very
long delay may occur while the Timer1
oscillator starts.
REGISTER 3-2: OSCCON: OSCILLATOR CONTROL REGISTER (ACCESS FD3h)
R/W-0 R/W-1 R/W-1 R/W-0 R-1
(1)
U-1 R/W-0 R/W-0
IDLEN IRCF2 IRCF1 IRCF0 OSTS —SCS1SCS0
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 7 IDLEN: Idle Enable bit
1 = Device enters Idle mode on SLEEP instruction
0 = Device enters Sleep mode on SLEEP instruction
bit 6-4 IRCF<2:0>: Internal Oscillator Frequency Select bits
When using INTOSC to drive the 4x PLL, select 8 MHz or 4 MHz only to avoid operating the 4x PLL
outside of specification.
111 = 8 MHz (INTOSC drives clock directly)
110 = 4MHz
(2)
101 = 2MHz
100 = 1MHz
011 = 500 kHz
010 = 250 kHz
001 = 125 kHz
000 = 31 kHz (from either INTOSC/256 or INTRC directly)
(3)
bit 3 OSTS: Oscillator Start-up Time-out Status bit
(1)
1 = Oscillator Start-up Timer time-out has expired; primary oscillator is running
0 = Oscillator Start-up Timer time-out is running; primary oscillator is not ready
bit 2 Unimplemented: Read as ‘1’
bit 1-0 SCS<1:0>: System Clock Select bits
11 = Postscaled internal clock (INTRC/INTOSC derived)
10 = Reserved
01 = Timer1 oscillator
00 = Primary clock source (INTOSC postscaler output when FOSC<2:0> = 001 or 000)
00 = Primary clock source (CPU divider output for other values of FOSC<2:0>)
Note 1: Reset value is ‘0’ when Two-Speed Start-up is enabled and ‘1’ if disabled.
2: Default output frequency of INTOSC on Reset (4 MHz).
3: Source selected by the INTSRC bit (OSCTUNE<7>).