Lock Detect Sequence - Motorola ColdFire MCF5281 User Manual

Start
with Tight Lock
Criteria
9.7.4.6 PLL Loss of Lock Conditions
Once the PLL acquires lock after reset, the LOCK and LOCKS flags are set. If the MFD is
changed, or if an unexpected loss of lock condition occurs, the LOCK and LOCKS flags
are negated. While the PLL is in the non-locked condition, the system clocks continue to
be sourced from the PLL as the PLL attempts to relock. Consequently, during the relocking
process, the system clocks frequency is not well defined and may exceed the maximum
system frequency, violating the system clock timing specifications.
However, once the PLL has relocked, the LOCK flag is set. The LOCKS flag remains
cleared if the loss of lock is unexpected. The LOCKS flag is set when the loss of lock is
caused by changing MFD. If the PLL is intentionally disabled during stop mode, then after
exit from stop mode, the LOCKS flag reflects the value prior to entering stop mode once
lock is regained.
9.7.4.7 PLL Loss of Lock Reset
If the LOLRE bit in the SYNCR is set, a loss of lock condition asserts reset. Reset
reinitializes the LOCK and LOCKS flags. Therefore, software must read the LOL bit in the
reset status register (RSR) to determine if a loss of lock caused the reset. See Section 28.4.2,
"Reset Status Register (RSR)."
To exit reset in PLL mode, the reference must be present, and the PLL must achieve lock.
MOTOROLA
Reference Count
≠
Feedback Count
Count N
Reference Cycles
and Compare
Number of Feedback
Cycles Elapsed
In Same Count/Compare Sequence
Figure 9-6. Lock Detect Sequence
Chapter 9. Clock Module
Loss of Lock Detected
Set Tight Lock Criteria
and Notify System of Loss
of Lock Condition
Reference Count =
Feedback Count = N
Reference Count =
Lock Detected.
Feedback Count = N + K
Set Relaxed Lock
IN Same Count/Compare Sequence
Condition and Notify
System of Lock
Condition
Functional Description
Reference Count
≠
Feedback Count
Count N + K
Reference Cycles
and Compare Number
of Feedback Cycles
Elapsed
9-15