Comtech EF Data SDM-2020 - Manual (Page 103)

SDM-2020 Satellite Modulator Revision 7
RS-422 Data Interface MN/SDM2020M.IOM
7-4
7.1.4 U
SER
I
NTERFACES
The following paragraphs describe the RS-422 user interfaces.
7.1.4.1 P
ARALLEL
, J3, DB25 F
EMALE
(DVB P
ARALLEL
/S
ERIAL
D
ATA
I
NTERFACE
)
This data port supports DVB and DBS parallel and serial packetized data. There are three
standard frame formats supported, as follows:
• None, no framing byte format: Continuous serial or parallel payload data with no
framing information.
• 188 byte format:
• Serial or parallel data, (1 sync byte + 187 payload bytes).
• 204 byte format:
• Serial or parallel data, (1 sync byte + 187 payload bytes + 16 bytes for
Reed-Solomon coding).
Figure 7-1 and Figure 7-2 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.
7.1.4.1.1 Connector Pinout, J3, Parallel/Serial DVB
The connector is a sub-miniature, 25-pin, female D connector, with threaded jack nuts
(refer to Table 7-2 for pinout). All signals on this connector are inputs to the modulator,
except the signal pair on pins 2 and 15 when the jumper is selected for SCT output.
When used as a serial data port, Data 7 (pins 3 and 16) are the active data pins. Signal
assignments for pins 2 and 15 are jumper-selectable. They are defined as signal ground in
the DVB definition of TM1449, but may be configured to provide SCT out.
Signal levels are as defined in RS-422. 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.
The same jumper provides the option for a TX or RX reference clock on connector J3
(pins 2 and 15). The pins are configured at the factory as signal ground per TM 1449. For
modulator applications where an SCT output is required in conjunction with using the
DVB Data port (J3), SCT may be jumped to pins 2 and 15, thus providing all signals on a
single connector.