Motorola MCF5281, MCF5282 user manual Loss of Clock in Stop Mode, Stop Mode Operation Sheet 1

Functional Description

Aspecial loss-of-clock condition occurs when both the reference and the PLL fail. The failures may be simultaneous, or the PLL may fail first. In either case, the reference clock failure takes priority and the PLL attempts to operate in SCM. If successful, the PLL remains in SCM until the next reset. If the PLL cannot operate in SCM, the system remains static until the next reset. Both the reference and the PLL must be functioning properly to exit reset.

9.7.4.11 Loss of Clock in Stop Mode

Table 9-10shows the resulting actions for a loss of clock in Stop Mode when the device is being clocked by the various clocking methods.

Table 9-10. Stop Mode Operation (Sheet 1 of 5)

LOCEN

LOCRE

LOLRE

OSC

FWKUP

Expected

LOCKSS

LOCK

LOCS

MODE

PLL

PLL

PLL Action

MODE

Comments

In

Action at

During Stop

Out

Stop

EXT

X

X

X

X

X

X

—

—

EXT

0

0

0

Lose reference

Stuck

—

—

—

clock

NRM

0

0

0

Off

Off

0

Lose lock,

Regain

NRM

‘LK

1

‘LC

f.b. clock,

No regain

Stuck

—

—

—

reference

clock

NRM

X

0

0

Off

Off

1

Lose lock,

Regain clocks, but

SCM–>

0–>‘L

0–>1

1–>‘L

Block LOCS and

f.b. clock,

don’t regain lock

unstable

K

C

LOCKS until

reference

NRM

clock and lock

clock

respectively

regain; enter

SCM regardless

of LOCEN bit

until reference

regained

No reference clock

SCM–>

0–>

0–>

1–>

Block LOCS and

regain

LOCKS until

clock and lock

respectively

regain; enter

SCM regardless

of LOCEN bit

No f.b. clock

Stuck

—

—

—

regain

MOTOROLA Chapter 9. Clock Module 9-17