3471-ddc.ib.rev2.doc
page 6 of 20
17/10/2007
Technical description DDC-3471
The DDC-3471 processes an SPI input and outputs processed SPI and ASI-C at the input data rate.
This module is capable of performing scrambling, de-scrambling, RS encoding, RS decoding, interleaving and de-
interleaving. It can encode as well as decode different MPEG TS formats. The module is normally set up as either a
decoder or an encoder. Combinations of both functions simultaneously are somewhat difficult and should be
avoided.
The processing functions are selected using three switches (interleaving, RS coding and scrambling) on the front
panel. Each switch has three positions (up, centre or down).
The DDC-3471 is internally divided into a decoder followed by an encoder.
A switch set to the UP position applies processing to the decoding section.
A switch set to the DOWN position applies processing to the encoding section.
A switch set to the CENTRE position does not perform that function to either the decoding or encoding
section.
Applying a function to both the decoder and encoder section simultaneously is prevented by means of each switch
having only three positions. Full encoding and decoding is possible by using two DDC-3471 modules connected
together, if this is ever required.
In most instances the DDC-3471 would be set to decoder mode with the de-interleaver and RS decoder functions
enabled.
To generate a FOXTEL compliant TS stream from a Rohde & Schwarz DVG, the DDC-3471 would be set with the
interleaver and RS encoder enabled.
SPI Output
The SPI output uses differential LVDS signalling with a standard 25 pin 'D' female connector.
The output is disabled when Input Loss Alarm is triggered.
ASI Output
ASI operates at 270 Mbit/s and uses 8B/10B coding with K28.5 stuffing bytes. The DDC-3471 implements the data
burst method of K28.5 stuffing. The ASI cable output uses a 75 Ohm BNC connector. A DVT/R-3210 optical link
can be used to transport the ASI-C signal via fibre optic cable.
See DVT/R-3210 brochure or manual for further
information.
Input Loss Alarms
The Input Loss Alarm will be asserted in the absence of SPI input clock.
Input TS Sync Error
After 2 consecutive TS syncs are missed a TS Sync Error is deemed to have occurred. The Sync error is reset only
after 5 consecutive TS syncs have been detected. The SYNC Error LED lights when a Sync error has been detected
and remains lit for approximately 300 ms after the Sync error has been reset.
188 TS Sync length indicator
If the number of bytes between TS syncs is 188 then the 188 LED lights.
204 TS Sync length indicator
If the number of bytes between TS syncs is 204 then the 204 LED lights.
Alarm relay
Alarm outputs are available on the rear assembly using the J 2 connector. N/O & N/C outputs can be selected using
LK 1. The relay is triggered upon loss of input or sync error. The N/O contact is preferred as it switches upon loss
of power or removal of the DDC-3471 from its rear assembly.
LED indicators 188 TS Byte length, 204 TS Byte length, CRC error, Scram present, RS present are blanked during
Input loss or sync loss.
IRT
Communications
www.irtcommunications.com