9-16
MCF5282 User’s Manual
MOTOROLA
Functional Description
In external clock mode, the PLL cannot lock. Therefore, a loss of lock condition cannot
occur, and the LOLRE bit has no effect.
9.7.4.8
Loss of Clock Detection
The LOCEN bit in the SYNCR enables the loss of clock detection circuit to monitor the
input clocks to the phase and frequency detector (PFD). When either the reference or
feedback clock frequency falls below the minimum frequency, the loss of clock circuit sets
the sticky LOCS flag in the SYNSR.
NOTE
In external clock mode, the loss of clock circuit is disabled.
9.7.4.9
Loss of Clock Reset
The clock module can assert a reset when a loss of clock or loss of lock occurs. When a
loss-of-clock condition is recognized, reset is asserted if the LOCRE bit in SYNCR is set.
The LOCS bit in SYNSR is cleared after reset. Therefore, the LOC bit must be read in RSR
to determine that a loss of clock condition occurred. LOCRE has no effect in external clock
mode.
To exit reset in PLL mode, the reference must be present, and the PLL must acquire lock.
Reset initializes the clock module registers to a known startup state as described in
Section 9.6, “Memory Map and Registers.”
9.7.4.10 Alternate Clock Selection
Depending on which clock source fails, the loss-of-clock circuit switches the system clocks
source to the remaining operational clock. The alternate clock source generates the system
clocks until reset is asserted. As Table 9-9 shows, if the reference fails, the PLL goes out of
lock and into self-clocked mode (SCM). The PLL remains in SCM until the next reset.
When the PLL is operating in SCM, the system frequency depends on the value in the RFD
field. The SCM system frequency stated in electrical specifications assumes that the RFD
has been programmed to binary 000.
If the loss-of-clock condition is due to PLL failure,
the PLL reference becomes the system clocks source until the next reset, even if the PLL
regains and relocks.
Table 9-9. Loss of Clock Summary
Clock
Mode
System Clock Source
Before Failure
Reference Failure Alternate Clock
Selected by LOC Circuit
1
Until Reset
1
The LOC circuit monitors the reference and feedback inputs to the PFD. See Figure 9-5.
PLL Failure Alternate Clock
Selected by LOC Circuit Until Reset
PLL
PLL
PLL self-clocked mode
PLL reference
External External
clock
None
NA
Summary of Contents for ColdFire MCF5281
Page 124: ...3 20 MCF5282 User s Manual MOTOROLA EMAC Instruction Set Summary ...
Page 141: ...MOTOROLA Chapter 5 Static RAM SRAM 5 5 SRAM Programming Model ...
Page 142: ...5 6 MCF5282 User s Manual MOTOROLA SRAM Programming Model ...
Page 168: ...6 26 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 186: ...7 18 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 228: ...9 22 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 246: ...10 18 MCF5282 User s Manual MOTOROLA Low Power Wakeup Operation ...
Page 254: ...11 8 MCF5282 User s Manual MOTOROLA Memory Map and Registers ...
Page 264: ...12 10 MCF5282 User s Manual MOTOROLA Chip Select Registers ...
Page 280: ...13 16 MCF5282 User s Manual MOTOROLA Misaligned Operands ...
Page 314: ...14 34 MCF5282 User s Manual MOTOROLA MCF5282 External Signals ...
Page 339: ...MOTOROLA Chapter 15 Synchronous DRAM Controller Module 15 25 SDRAM Example ...
Page 340: ...15 26 MCF5282 User s Manual MOTOROLA SDRAM Example ...
Page 356: ...16 16 MCF5282 User s Manual MOTOROLA DMA Controller Module Functional Description ...
Page 408: ...17 52 MCF5282 User s Manual MOTOROLA Buffer Descriptors ...
Page 446: ...20 24 MCF5282 User s Manual MOTOROLA Interrupts ...
Page 474: ...22 18 MCF5282 User s Manual MOTOROLA Programming Model ...
Page 510: ...23 36 MCF5282 User s Manual MOTOROLA Operation ...
Page 526: ...24 16 MCF5282 User s Manual MOTOROLA I2C Programming Examples ...
Page 672: ...28 12 MCF5282 User s Manual MOTOROLA Functional Description ...
Page 718: ...29 46 MCF5282 User s Manual MOTOROLA Motorola Recommended BDM Pinout ...
Page 750: ...32 8 MCF5282 User s Manual MOTOROLA Ordering Information ...