DSPIC30F6010 MICROCHIP [Microchip Technology], DSPIC30F6010 Datasheet - Page 142

• Manufacturer Part Number: DSPIC30F6010
• Description: High-Performance Digital Signal Controllers
• Manufacturer: MICROCHIP [Microchip Technology]

dsPIC30F6010
If the oscillator has a very slow start-up time coming
out of POR, BOR or Sleep, it is possible that the
PWRT timer will expire before the oscillator has
started. In such cases, the FSCM will be activated and
the FSCM will initiate a Clock Failure Trap, and the
COSC<1:0> bits are loaded with FRC oscillator selec-
tion. This will effectively shut-off the original oscillator
that was trying to start.
The user may detect this situation and restart the
oscillator in the Clock Fail Trap ISR.
Upon a clock failure detection, the FSCM module will
initiate a clock switch to the FRC Oscillator as follows:
1.
2.
3.
For the purpose of clock switching, the clock sources
are sectioned into four groups:
1.
2.
3.
4.
The user can switch between these functional groups,
but cannot switch between options within a group. If the
primary group is selected, then the choice within the
group is always determined by the FPR<3:0>
configuration bits.
The OSCCON register holds the CONTROL and
STATUS bits related to clock switching.
• COSC<1:0>: Read only status bits always reflect
• NOSC<1:0>: Control bits which are written to
• LOCK: The LOCK status bit indicates a PLL lock.
• CF: Read only status bit indicating if a clock fail
• OSWEN: Control bit changes from a ‘0’ to a ‘1’
DS70119D-page 140
the current oscillator group in effect.
indicate the new oscillator group of choice.
- On POR and BOR, COSC<1:0> and
detect has occurred.
when a clock transition sequence is initiated.
Clearing the OSWEN control bit will abort a clock
transition in progress (used for hang-up
situations).
The COSC bits (OSCCON<13:12>) are loaded
with the FRC Oscillator selection value.
CF bit is set (OSCCON<3>).
OSWEN control bit (OSCCON<0>) is cleared.
Primary
Secondary
Internal FRC
Internal LPRC
NOSC<1:0> are both loaded with the
Configuration bit values FOS<1:0>.
Preliminary
If configuration bits FCKSM<1:0> = 1x, then the clock
switching and fail-safe clock monitor functions are
disabled. This is the default configuration bit setting.
If clock switching is disabled, then the FOS<1:0> and
FPR<3:0> bits directly control the oscillator selection
and the COSC<1:0> bits do not control the clock
selection. However, these bits will reflect the clock
source selection.
21.2.8
A write to the OSCCON register is intentionally made
difficult because it controls clock switching and clock
scaling.
To write to the OSCCON low byte, the following code
sequence must be executed without any other
instructions in between:
• Byte Write “0x46” to OSCCON low
• Byte Write “0x57” to OSCCON low
Byte Write is allowed for one instruction cycle. Write the
desired value or use bit manipulation instruction.
To write to the OSCCON high byte, the following
instructions must be executed without any other
instructions in between:
• Byte Write “0x78” to OSCCON high
• Byte Write “0x9A” to OSCCON high
Byte Write is allowed for one instruction cycle. Write the
desired value or use bit manipulation instruction.
Note:
The application should not attempt to
switch to a clock of frequency lower than
100 KHz when the fail-safe clock monitor is
enabled. If such clock switching is
performed, the device may generate an
oscillator fail trap and switch to the Fast RC
oscillator.
PROTECTION AGAINST
ACCIDENTAL WRITES TO OSCCON
 2004 Microchip Technology Inc.