Introduction
HE4000 Encoding System
2.4.2 Clock Interface Configuration 2
If the DTE cannot turn around the ST, but has an internal clock source that can be provided as TT
to the HE4000, use this option to configure the auxiliary data channel.
The following block diagram shows the clock configuration for a DTE providing an internal clock
source as TT to the HE4000.
DT E
HE 4000
Data
Tim ing Data
Data SD
SD
Latching Data
To TTM
Int. Source
Clock TT
Ext. Source
TT
Switch
Internal Clock
Clock ST
Int. Source
ST
Internal Clock ST
In this configuration, the DTE clock is set to internal and the HE4000 auxiliary data channel clock
source is set to external. The DTE uses its internal clock source to time the data, sends the data
to the HE4000 on SD, and sends its internal clock to the HE4000 as TT. The HE4000 uses TT to
latch the data. The HE4000 auxiliary data channel must be configured for an external clock
source.
2.4.3 Clock Interface Configuration 3
If the DTE cannot turn around the ST, and does not have an internal clock source that can be
provided as TT to the HE4000, configure the HE4000 to use the ST to latch the data. However,
this scenario is not recommended and should be considered only if neither of the other two-clock
source configurations can be used.
The following block diagram shows the clock configuration for a DTE configured for an external
clock and a HE4000 auxiliary data channel configured for an internal clock.
DT E
HE 4000
Data
Tim ing Data
Data SD
SD
Latching Data
To TTM
Ext. Source
TT
Switch
Clock ST
Int. Source
ST
Internal Clock ST
In this scenario, both the DTE and the HE4000 use ST, but the ST is provided to the DTE on one
path and to the HE4000 on a different path. Depending upon the length of cable between the
DTE and the HE4000, the clock may be received out of phase at the HE4000. The longer the
cable, the further out of phase the clock will be.
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01-0951-404 Rev B
