Comtech EF Data SDM-2020 - Manual (Page 32)

SDM-2020 Satellite Demodulator Revision 4
Introduction MN/SDM2020D.IOM
1–6
1.4.2 Transmit/Receive Data
The data format for the transmit ( TX ) and receive (RX) data interfaces are the same.
There are three general modes of operation:
• None (187)
• 188
• 204
When None (187) mode is selected,
no frame structure is expected, while the 188 and 204
modes will synchronize to standard MPEG-2 transport frames. Other supported data
formats are referenced in the appropriate section of this appendix, but the data from other
frame formats is extracted and converted to one of the three modes of operation.
Figure 1-3 and Figure 1-4 depict the 204-byte packetization for byte parallel and byte
serial formats, showing all possible data fields and timing signal relationships. The 188
byte and no framing formats are subsets of the 204 byte format.
1 Byte Sync 1 Byte Sync 187 Bytes Payload
SYNC
DATA
DVALID
CLOCK
SYNC 1 SYNC 1 187 1 16
16 RS Bytes
Figure 1-3. 204 Byte Parallel Format
0 1 0 0 1 0 1 1
8 Bits Sync 1496 Bits Payload
SYNC
DATA
DVALID
CLOCK
0 1 0 0 1 0 1 1
8 Bits Sync 128 Bits RS
Figure 1-4. 204 Byte Serial Format