HE4000 Encoding System
Introduction
2.4 Configuring the DTE and HE4000 Clock Interfaces
After you have cabled the data termination equipment (DTE) to the HE4000, you must determine
the most effective HE4000 and DTE clock source arrangements. There are four different ways to
resynchronize both SD and HD video channel timing references:
2.4.1 Clock Interface Configuration 1
The most reliable auxiliary data channel clock source configuration requires the DTE to provide a
clock (TT) synchronous with the data (SD) to the HE4000. This scenario allows the HE4000 to
latch the data using a clock that has traveled the same path as the data, which ensures that both
the clock and the data are received in phase at the HE4000.
The following block diagram shows the clock configuration for a DTE configured to turn around
the ST clock source, and a HE4000 auxiliary data channel configured for an external clock
source.
Notice in the illustration that the switch for the HE4000 auxiliary data channel clock source is
configured for external even though the HE4000 is providing ST to the DTE.
DTE
HE4000
Data
Tim ing Data
Data 80
SD
Latching D ata
To TTM
Int. Source
ST
Switch
Clock TT
Ext. Source
TT
Switch
Internal Clock
Ext. Source
Clock ST
Int. Source
ST
Internal Clock ST
In this configuration, the HE4000 provides clock (ST) to the DTE. The switch for the DTE clock
source is configured to accept the external clock (ST) provided by the HE4000. The DTE uses the
ST to time the data, sends the data to the HE4000 on SD, and returns the ST to the HE4000 on
TT. The HE4000 uses TT to latch the data.
The HE4000 auxiliary data channel must be configured for an external clock source to accept TT
from the DTE.
01-0951-404 Rev B
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