Cirrus Logic CS2000-CP - Manual (Page 16)

CS2000-CP
16 DS761F2
Regardless of the setting of the ClkSkipEn bit the PLL output will continue for 2
23
SysClk cycles (466 ms
to 1048 ms) after CLK_IN is removed (see Figure 13 ). This is true as long as CLK_IN does not glitch or
have an effective change in period as the clock source is removed, otherwise the PLL will interpret this as
a change in frequency causing clock skipping and the 2
23
SysClk cycle time-out to be bypassed and the
PLL to immediately unlock. If the prior conditions are met while CLK_IN is removed and 2
23
SysClk cycles
pass, the PLL will unlock and the PLL_OUT state will be determined by the ClkOutUnl bit; See “PLL Clock
Output” on page 23 . If CLK_IN is re-applied after such time, the PLL will remain unlocked for the specified
time listed in the “AC Electrical Characteristics” on page 8 after which lock will be acquired and the PLL
output will resume.
If it is expected that CLK_IN will be removed and then reapplied within 2
23
SysClk cycles but later than
t
CS
, the ClkSkipEn bit should be disabled. If it is not disabled, the device will behave as shown in
Figure 14 ; note that the lower figure shows that the PLL output frequency may change and be incorrect
without an indication of an unlock condition.
Figure 13. CLK_IN removed for > 2
23
SysClk cycles
CLK_IN
PLL_OUT
UNLOCK
ClkSkipEn=0 or 1
ClkOutUnl=0
Lock Time
CLK_IN
PLL_OUT
UNLOCK
ClkSkipEn=0 or 1
ClkOutUnl=1
Lock Time
= invalid clocks
2 23 SysClk cycles 2 23 SysClk cycles
CLK_IN
PLL_OUT
UNLOCK
ClkSkipEn=0 or 1
ClkOutUnl=0
Lock Time
CLK_IN
PLL_OUT
UNLOCK
ClkSkipEn=0 or 1
ClkOutUnl=1
Lock Time
t
CS
t
CS
= invalid clocks
CLK_IN
PLL_OUT
UNLOCK
ClkSkipEn= 1
ClkOutUnl= 0 or 1
Lock Time
t
CS
= invalid clocks
2 23 SysClk cycles 2 23 SysClk cycles
2 23 SysClk cycles
Figure 14. CLK_IN removed for < 2
23
SysClk cycles but > t
CS