Comtech EF Data SDM-2020 - Manual (Page 119)

SDM-2020 Satellite Modulator Revision 7
ASI/RS-422 Data Interface MN/SDM2020M.IOM
9-4
Table 9-1. ASI/RS-422 Specifications (Continued)
RS-422 Specifications
Signal
Types SD, TT, ST, RD, RT, RS, RR, CS, DM, and MC.
Data synchronization is detected by correlating the data stream for the MPEG2 sync pattern
per ETS 300 421.
Voltage
Level 4 ± 2V differential into 100 Ω.
Notes:
1. Loopback – The yellow TEST MODE LED is illuminated when Loopback is turned
ON. During Loopback input data is looped back to the terrestrial data output
connector(s) and data continues into the modulator.
Loop Thru – Operation is nearly identical to Loopback, except the yellow LED is not
illuminated. Conceptually, the data output is operating as a monitor point.
2. Rev. A or later assemblies include this capability. Rev dash (-) assemblies can be
upgraded to this capability.
9.1.3 T
RANSMIT
I
NPUT
C
ONNECTORS
, J3/J4, BNC, F
EMALE
These two connectors accept TX data from the terrestrial interface. By default, J3 is
enabled and J4 is disabled. The active input is user programmable and maintained in non-
volatile memory of the modulator or demodulator chassis. Both connectors are terminated
into 75
Ω whether selected or not selected.
9.1.4 RS-422 C
ONNECTOR
, J5, 25-
PIN
D, F
EMALE
This connector is compatible with EIA-530 operation and pinout. It is a serial interface
with RS-422 signals plus the TTL-OC fault signals indicating the status of the modulator
or demodulator
.
9.1.4.1 C
ONNECTOR
P
INOUT
J5
The connector is a 25-pin, female, D type, with threaded jack nuts.
Notes:
1. RS-422 signal levels are as defined in RS-422.
2. The differential sense of all signal pairs is a logic “1” when “A” is negative
with respect to “B.”
Single-ended signals (MF and DF fault signals) are open collector where: