Comtech EF Data SDM-2020 User Manual
Page 129
SDM-2020 Satellite Modulator
Revision 7
ECL/HSSI TX
MN/SDM2020M.IOM
10-8
10.1.4.3
T
ERRESTRIAL
E
XTENDED
S
IGNAL
D
EFINITION
The HSSI specification has no provision for SYNC or DVALID signals. If terrestrial data
framing is desired, a sync byte (47 hex) is embedded into the data stream every 188 or
204 bytes, as selected in the modulator configuration. The modulator detects the sync
byte and formats the serial interface into a standard, error-protected 204-byte packet. In
order to support TM1449, PSYNC and DVALID are routed to RESERVED (from DCE)
HSSI pins. Refer to Table 10-4 for definition of signals.
Table 10-4. Definition of Signals
Signal
Definition
Transmitter
Synchronization
(TX PSYNC)
Indicates the beginning of a transport packet by signaling the SYNC byte. Active per
defined format timing.
Transmitter Data Valid
(TX DVALID)
Indicates valid data at the interface. Active per defined format timing.
Carrier Detect
(CD)
Indicates Demodulator carrier-tracking loop locked. Status output. TTL output. Active
High (programmable).
Demodulator Fault
(DF)
Open collector TTL signal indicating Demodulator Fault. Active High. External pull-up
required.
Modulator Fault
(MF)
Open collector TTL signal indicating Modulator Fault. Active High. External pull-up
required.
Receiver
Synchronization
(RX PSYNC)
Indicates the beginning of a transport packet by signaling the SYNC byte. Active per
defined format timing.
Receiver Data Valid
(RX DVALID)
Indicates valid data at the interface. Active per defined format timing.