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Data Interfaces
A.3.4
User Interfaces
The following paragraphs describe the electrical and physical interfaces, which support
terrestrial data and auxiliary information on the LVDS data interface module.
A.3.4.1
Receive/Transmit Data, J3/J4, DB25 Female
There are three general modes of operation controlled via the front panel display/keypad
or the remote port. The standard frame formats supported are as follows:
•
•
•
Figure A-1 and depict the 204 byte packetization for byte parallel and byte serial formats
at J3 and J4, showing all possible data fields and timing signal relationships.
The 188 byte and no framing formats are subsets of the 204 byte format used over the
satellite.
A.3.4.1.1
Connector Pinouts, J3
Note: Table A-8 provides applicable data for the SDM-2020 Demodulator.
The connector is sub-miniature 25-pin D female, with threaded jack nuts.
All signals for this connector are outputs from the Demodulator, except the signal pair on
pins 2 and 15 (for an exception, see Figure A-4, for jumper settings).
When used as a serial data port, Data 7 (pins 3 and 16) are the active data pins. For DVB
parallel operation, Data 7 through Data 8 are used.
Signal levels are as defined in TIA/EIA-644. Per TM1449, the differential sense of all
signal pairs is a logic "1" when "A" is positive with respect to "B". This is the normal
selection in the Configuration Interface menu (see Chapter 3). For DBS applications, the
polarity of signals may be inverted from the Configuration Interface menu.
A–16
188 Mode: The unit outputs a DVB/MPEG2 frame consisting of 1 sync byte
(047 hex) and 187 bytes of data. The 16 bytes of Reed-Solomon check data are
removed by the demodulator and the 188 byte frame returned to the terrestrial
circuit.
204 Mode: A 204 byte frame structure consisting of 1 sync byte (047 hex) plus
187 bytes of data and 16 bytes reserved for check bytes is output. The
demodulator returns the 204 byte frame to the terrestrial circuit.
None: In this mode, no frame structure is output. The demodulator removes the
16 Reed-Solomon bytes and the sync byte and returns the data to the terrestrial
circuit.
SDM-2020 Satellite Demodulator
Rev.3
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