Si53xx-RM
Rev. 0.52
93
For cases where phase skew is required, see Section “7.7. Output Phase Adjust (Si5326, Si5368)” for more details
on controlling the sync input to sync output phase skew via the
FSYNC_SKEW
[16:0] bits. See Section
“8.2. Output
Clock Drivers” for information on the FS_OUT signal format, pulse width, and active logic level control.
7.8.2. FSYNC Skew Control (Si5368)
When CKIN3 and CKIN4 are configured as frame sync inputs (
CK_CONFIG_REG
= 1), phase skew of the sync
input active edge to FS_OUT active edge is controllable via the
FSYNC_SKEW
[16:0] register bits. Skew control
has a resolution of 1/f
CKOUT2
and a range of 131,071/f
CKOUT2
. The entered skew value must be less than the
period of CKIN3, CKIN4, and FS_OUT.
The skew should not be changed more than once per FS_OUT period. If a FSYNC realignment is being made, the
skew should not be changed until the realignment is complete. The skew value and the FS_OUT pulse width
should not be changed within the same FS_OUT period.
Before writing the three bytes needed to specify a new
FSYNC_SKEW
[16:0] value, the user should set the register
bit
FSKEW_VALID
= 0. This causes the alignment state machine to keep using the previous
FSYNC_SKEW
[16:0]
value, ignoring the new register values as they are being written. Once the new
FSYNC_SKEW
[16:0] value has
been completely written, the user should set
FSKEW_VALID
= 1 at which time the alignment state machine will
read the new skew alignment value. Note that when the new
FSYNC_SKEW
[16:0] value is used, a phase step will
occur in FS_OUT.
7.8.3. Including FSYNC Inputs in Clock Selection (Si5368)
The frame sync inputs, CKIN3 and CKIN4, are both monitored for loss-of-signal (
LOS3_INT
and
LOS4_INT
)
conditions. To include these LOS alarms in the input clock selection algorithm, set
FSYNC_SWTCH_REG
= 1. The
LOS3_INT
is logically ORed with
LOS1_INT
and
LOS4_INT
is ORed with
LOS2_INT
as inputs to the clock
selection state machine. If it is desired not to include these alarms in the clock selection algorithm, set
FSYNC_SWTCH_REG
= 0. The frequency offset (FOS) alarms for CKIN1 and CKIN2 can also be included in the
state machine decision making as described in Section “7.11. Alarms (Si5319, Si5324, Si5325, Si5326, Si5327,
Si5367, Si5368, Si5369, Si5374, Si5375)”; however, in frame sync mode (
CK_CONFIG_REG
= 1), the FOS alarms
for CKIN3 and CKIN4 are ignored.
7.8.4. FS_OUT Polarity and Pulse Width Control (Si5368)
Additional output controls are available for FS_OUT. The active polarity of FS_OUT is set via the
FS_OUT_POL
register bit and the active duty cycle is set via the
FSYNC_PW
[9:0] register. Pulse width settings have a resolution
of 1/f
CKOUT2
, and a 50% duty cycle setting is provided. Pulse width settings can range from 1 to (NC5-1) CKOUT2
periods, providing the full range of pulse width possibilities for a given NC5 divider setting.
The FS_OUT pulse should not be changed more than once per FS_OUT period. If a FSYNC realignment is being
made, the pulse width should not be changed until the realignment is complete. The FS_OUT pulse width and the
skew value should not be changed within the same FS_OUT period.
Before writing a new value into
FSYNC_PW
[9:0], the user should set the register bit
FPW_VALID
= 0. This causes
the FS_OUT pulse width state machine to keep using the previous
FSYNC_PW
[9:0] value, ignoring the new
register values as they are being written. Once the new
FSYNC_PW
[9:0] value has been completely written, the
user should set
FPW_VALID
= 1, at which time the FS_OUT pulse width state machine will read the new pulse
width value.
Writes to
NC5_LS
should be treated the same as writes to
FSYNC_PW
. Thus, all writes to
NC5_LS
should occur
only when
FPW_VALID = 0
. Any such writes will not take effect until
FPW_VALID = 1
.
Note that f
CKOUT2
must be less than or equal to 710 MHz when CK_CONFIG_REG = 1; otherwise, the FS_OUT
buffer and NC5 divider must be disabled.
7.8.5. Using FS_OUT as a Fifth Output Clock (Si5368)
In applications where the frame synchronization functionality is not needed (
CK_CONFIG_REG
= 0), FS_OUT can
be used as a fifth clock output. In this case, no realignment requests should be made to the NC5 divider (hold
FS_ALIGN
= 0 and
FSYNC_ALIGN_REG
= 0). Output pulse width and polarity controls for FS_OUT are still
available as described above. The 50% duty cycle setting would be used to generate a typical balanced output
clock.
Summary of Contents for Si5316 Series
Page 2: ...Si53xx RM 2 Rev 0 52 ...
Page 110: ...Si53xx RM 110 Rev 0 52 Figure 48 sfout_5 LVPECL Figure 49 sfout_6 CML ...
Page 111: ...Si53xx RM Rev 0 52 111 Figure 50 sfout_7 LVDS ...
Page 127: ...Si53xx RM Rev 0 52 127 Figure 66 155 52 MHz In 622 08 MHz Out Loop BW 7 Hz Si5324 ...
Page 128: ...Si53xx RM 128 Rev 0 52 Figure 67 19 44 MHz In 156 25 MHz Out Loop BW 80 Hz ...
Page 129: ...Si53xx RM Rev 0 52 129 Figure 68 19 44 MHz In 156 25 MHz Out Loop BW 5 Hz Si5324 ...
Page 131: ...Si53xx RM Rev 0 52 131 Figure 70 61 44 MHz In 491 52 MHz Out Loop BW 7 Hz Si5324 ...
Page 132: ...Si53xx RM 132 Rev 0 52 Figure 71 622 08 MHz In 672 16 MHz Out Loop BW 6 9 kHz ...
Page 133: ...Si53xx RM Rev 0 52 133 Figure 72 622 08 MHz In 672 16 MHz Out Loop BW 100 Hz ...
Page 134: ...Si53xx RM 134 Rev 0 52 Figure 73 156 25 MHz In 155 52 MHz Out ...
Page 139: ...Si53xx RM Rev 0 52 139 Figure 78 86 685 MHz In 173 371 MHz Out ...
Page 140: ...Si53xx RM 140 Rev 0 52 Figure 79 86 685 MHz In 693 493 MHz Out ...
Page 142: ...Si53xx RM 142 Rev 0 52 Figure 81 10 MHz In 1 GHz Out ...
Page 174: ...Si53xx RM 174 Rev 0 52 Figure 99 Si5374 Si5375 DSPLL A ...
Page 175: ...Si53xx RM Rev 0 52 175 Figure 100 Si5374 Si5375 DSPLL B ...
Page 176: ...Si53xx RM 176 Rev 0 52 Figure 101 Si5374 Si5375 DSPLL C ...