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GS4901B/GS4900B Preliminary Data Sheet
37703 - 0
April 2006
45 of 95
NOTE 2: When locking the SD input reference standards 3, 5, 7, or 9 to the
“f/1.001”
HD input reference standards, there may be a random phase difference
between the input VSYNC and output V Sync signals occuring each time the input
reference is removed and re-applied. This will affect all line-based timing outputs.
The user may reset the line-based counters after the reference is re-applied
without disrupting the pixel or audio clocks by toggling bit 15 of register address
83h in the host interface. This will cause the input VSYNC and line-based timing
output signals to take on their default timing relationship, as described in Note 3 of
Section 3.2.1.1 on page 35
.
Re-acquisition of the Same Reference
Upon re-application of the reference signal, the device checks whether the
reference has drifted more than +/- 2us from its expected location by comparing
the current relative position of the H pulses with the previous position, over a
16-line interval. If the reference returns with the H pulses in the expected location
+/- 2us, the PLL will drift lock and the clock generator will continue to operate
without a glitch. The REF_LOST and LOCK_LOST pins will be set back LOW.
If the reference returns with the H pulses outside the +/- 2us window, the device
will crash lock the output timing to the new input phase. The principles of crash lock
and drift lock are described in
Section 3.6.1 on page 47
.
NOTE: To resume proper genlock operation upon re-application of the reference
signal, the user must implement the following register manipulation every time the
reference is removed and re-applied:
1. Read the value contained in register address 24h
2. Clear the Run_Window bits [2:0] of register 24h
3. Re-write the value read in step 1 to register address 24h.
This procedure will force the device to lock to the reference as described above,
but will maintain the flywheeling capability of the GS4901B/GS4900B should a
single missing H pulse occur in the genlocked state.
To avoid the above procedure, the user may choose to clear the Run_Window bits
[2:0] of register address 24h upon power-up or reset. However, this will disable the
flywheeling feature of the device that allows it to maintain genlock through one
missing input H pulse.
Acquisition of a New Reference
When a new reference is applied, the device continues to operate in Freeze mode
while the reference format detector checks for validity as described in
Section 3.5.2
on page 43
. Once validity is detected, the REF_LOST pin is set LOW.
Assuming GENLOCK is LOW, the device will then attempt to genlock the selected
output clock and timing signals to the new input reference. If the output can be
automatically genlocked to the new input reference, LOCK_LOST will go LOW and
the device will re-enter Genlock mode. Otherwise, the LOCK_LOST pin will remain
HIGH and the device will enter Free Run mode.