Comtech EF Data SDM-2020 - Manual (Page 98)

SDM-2020 Satellite Modulator Revision 7
Data Interfaces MN/SDM2020M.IOM
6-4
Note: For proper operation, data and timing must be continuous, and meet the described criteria as
specified in Figure 6-1, Figure 6-2, and Table 6-2.
Table 6-2. 204 Data and Timing
DATA Payload data is byte parallel, where DATA 7 is the most significant bit; or byte serial,
where data is applied to DATA 7 with the most significant bit preceding the least.
For 188 and 204 format, the payload is 187 bytes in length, preceded by a sync word. In
the 204-byte mode, the payload is followed by 16 bytes of reed-Solomon data, or 16 filler
bytes.
CLOCK The clock is at the bit or byte rate in accordance with serial or parallel mode. The rising
edge of the clock is centered on the data.
SYNC SYNC timing depends upon the selection made for DVB FRAMING TYPE in the
Configuration Interface menu
DVB Framing Type SYNC
188 or 204 The SYNC timing is derived from either the EXT SYNC or
CORR ON DATA selection from the Configuration Interface
menu. See the TX SYNC SELECT command, Appendix A.
None The SYNC signal is ignored.
For the 188 or 204 byte framing modes, either a SYNC pulse or SYNC byte of value 47h
is required, dependent on the modulator configuration. Both may be applied, with only
one having effect, dependent upon configuration. When used, the SYNC pulse is active
high centered over the SYNC word. In parallel operation, it is one byte clock width. In
serial operation, the modulator recognizes the SYNC pulse centered on the entire SYNC
bit (8 clocks wide), or centered on the most significant bit of the byte (1 clock wide).
DVALID Although this signal is identified by both DVB and DBS formats, it is not used by the
modulator.