PIC18F6X2X Datasheet, PDF (27/386 Pages) Microchip Technology – 64/80-Pin High Performance, 64-Kbyte Enhanced FLASH Microcontrollers with A/D

PIC18F6X2X/8X2X
2.6.1 SYSTEM CLOCK SWITCH BIT
The system clock source switching is performed under
software control. The system clock switch bits,
SCS1:SCS0 (OSCCON<1:0>), control the clock
switching. When the SCS0 bit is ‘0’, the system clock
source comes from the main oscillator that is selected
by the FOSC configuration bits in CONFIG1H Configu-
ration register. When the SCS0 bit is set, the system
clock source will come from the Timer1 oscillator. The
SCS0 bit is cleared on all forms of RESET.
When FOSC bits are programmed for Software PLL
mode, SCS1 bit can be used to select between primary
oscillator/clock and PLL output. SCS1 bit will only have
an effect on the system clock if the PLL is enabled
(PLLEN = 1) and locked (LOCK = 1), else it will be
forced cleared. When programmed with Configuration
Controlled PLL, SCS1 bit will be forced clear.
REGISTER 2-1: OSCCON REGISTER
U-0
U-0
U-0
—
—
—
bit 7
Note:
The Timer1 oscillator must be enabled
and operating to switch the system clock
source. The Timer1 oscillator is enabled
by setting the T1OSCEN bit in the Timer1
Control register (T1CON). If the Timer1
oscillator is not enabled, then any write to
the SCS0 bit will be ignored (SCS0 bit
forced cleared) and the main oscillator will
continue to be the system clock source.
U-0
R/W-0 R/W-0 R/W-0 R/W-0
—
LOCK PLLEN SCS1 SCS0
bit 0
bit 7-4
bit 3
bit 2
bit 1
bit 0
Unimplemented: Read as ‘0’
LOCK: Phase Lock Loop Lock Status bit
1 = Phase lock loop output is stable as system clock
0 = Phase lock loop output is not stable and output cannot be used as system clock
PLLEN⁽¹⁾: Phase Lock Loop Enable bit
1 = Enable phase lock loop output as system clock
0 = Disable phase lock loop
SCS1: System Clock Switch bit 1
When PLLEN and LOCK bits are set:
1 = Use PLL output
0 = Use primary oscillator/clock input pin
When PLLEN or LOCK bit is cleared:
Bit is forced clear.
SCS0⁽²⁾: System Clock Switch bit 0
When OSCSEN configuration bit = 0 and T1OSCEN bit = 1:
1 = Switch to Timer1 oscillator/clock pin
0 = Use primary oscillator/clock input pin
When OSCSEN and T1OSCEN are in other states:
Bit is forced clear.
Note 1: PLLEN bit is forced set when configured for ECIO+PLL and HS+PLL. This bit is
writable for ECIO+SPLL and HS+SPLL modes only; forced cleared for all other
Oscillator modes.
2: The setting of SCS0 = 1 supersedes SCS1 = 1.
Legend:
R = Readable bit
- n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared x = Bit is unknown
 2003 Microchip Technology Inc.
Advance Information
DS39612A-page 25