Comtech EF Data QAM256 - Manual (Page 36)

Rear Panel Interfaces QAM256 Digital Video Modulator and Upconverter
5-4 TM077 - Rev. 4.0
5.5 ASI/Parallel Interface Connections
5.5.1 TX PARALLEL Connector
The RS-422 Transmit Parallel Connector (J1) is a 25-Pin Female D-Sub Connector. The pinouts
are listed in Table 5-3.
5.5.2 REMOTE Connector
The RS-485 Remote Connector (J3) is a 9-Pin Female D-Sub Connector. The pinouts are listed
in Table 5-2.
5.5.3 TX ASI Connector
The Transmit ASI Connector (J4) is a Female BNC Connector.
5.6 ASI and Advanced ASI Interfaces
The QAM256 has two ASI options that apply to different uses. The Normal ASI option interfaces
to data sources that conform to the DVB ASI Specification. The DVB ASI Specification requires
data sources to transmit the ASI/DVB transport stream at a constant data rate and packet gap
with no variation in time from one sync byte to the next.
The Advanced ASI Option is designed to interface with data sources that do not conform to the
DVB ASI Specification. This card will handle transport streams with inconsistent data rates or
packet gaps. The modulator’s data rate must be set greater than the fastest data rate that can be
expected from the data source. When the data is not available at that data rate, the modulator
will output DVB Null Frames (see Table 5-4) until enough data has been received to fill a packet.
In this method, the modulator’s input buffer will not be overrun and the demodulator will not lose
lock due to inconsistent packet delivery.
Table 5-4. DVB Null Packet Description
Null Packet = Sync Byte PID Count Data
Hex Value 47 IFFF 0000 FF - FF
Byte Number 0 1 - 2 3 - 4 5 - 187