PIC24FJ128GA010_09 Datasheet, PDF (100/240 Pages) Microchip Technology – 64/80/100-Pin General Purpose, 16-Bit Flash Microcontrollers

PIC24FJ128GA010 FAMILY
A recommended code sequence for a clock switch
includes the following:
1. Disable interrupts during the OSCCON register
unlock and write sequence.
2. Execute the unlock sequence for the OSCCON
high byte, by writing 78h and 9Ah to
OSCCON<15:8> in two back-to-back
instructions.
3. Write new oscillator source to the NOSC control
bits in the instruction immediately following the
unlock sequence.
4. Execute the unlock sequence for the OSCCON
low byte by writing 46h and 57h to
OSCCON<7:0> in two back-to-back instructions.
5. Set the OSWEN bit in the instruction immediately
following the unlock sequence.
6. Continue to execute code that is not clock
sensitive (optional).
7. Invoke an appropriate amount of software delay
(cycle counting) to allow the selected oscillator
and/or PLL to start and stabilize.
8. Check to see if OSWEN is ‘0’. If it is, the switch
was successful. If OSWEN is still set, then
check the LOCK bit to determine cause of
failure.
The core sequence for unlocking the OSCCON register
and initiating a clock switch is shown in Example 7-1.
EXAMPLE 7-1:
BASIC CODE SEQUENCE
FOR CLOCK SWITCHING
;Place the new oscillator selection in W0
;OSCCONH (high byte) Unlock Sequence
MOV
#OSCCONH, w1
MOV
#0x78, w2
MOV
#0x9A, w3
MOV.b
w2, [w1]
MOV.b
w3, [w1]
;Set new oscillator selection
MOV.b
WREG, OSCCONH
;OSCCONL (low byte) unlock sequence
MOV
#OSCCONL, w1
MOV
#0x46, w2
MOV
#0x57, w3
MOV.b
w2, [w1]
MOV.b
w3, [w1]
;Start oscillator switch operation
BSET OSCCON, #0
DS39747E-page 100
© 2009 Microchip Technology Inc.