Specifications

8-VSB Agile Modulator Issue 1.02 December 9, 2008 Page 16 of 29
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Data Input Interfaces
The module accepts an MPEG2-Transport Stream dedicated to ATSC transmission as
specified in SMPTE-310M and ATSC Standard A/53. It also supports an ASI-320 (DVB-
ASI) stream format. The two data inputs are implemented to allow for input data stream
redundancy (Primary input / Secondary input).
Data Input Management
Bit Rate Adaptation and PCR (Program Clock Reference) Re-Stamping
The ATSC transmission scheme relies on a very stable and accurate data stream
clock. The SMPTE-310 data clock will be at the exact standardized clock frequency.
At the same time, the modulator will synchronize with this input data stream to be
able to recover the same clock. In the case of using an external clock reference (10
MHz), the global clock synchronization might be plesiochronous (i.e. a small clock
deviance between the multiplexer clock and the modulator reference clock). In that
case, it is recommended to enable the “bit rate adaptation” on the modulator. When
this mode of operation is enabled, the unit discards or inserts null packets to adapt
the MPEG transport stream input bit rate to the precise bit rate defined by the ATSC
mode. PCR re-stamping is then executed accordingly.
Switching Performance:
The switching is not expected to be seamless. However, in the case of feeding the
exact same data stream on both inputs (Primary & Secondary), the modulator will
perform seamless switching from one input to the other. Switching is made on a per
packet basis.
Automatic Mute:
The user can enable or disable the automatic mute for when an error on either the
SMPTE-310 or the ASI-320 input is detected. The delay for the detection of the loss
of the SMPTE-310 input is 1 second. In case the user disables the automatic mute,
null packets are inserted to reach the required bit rate.