Comtech EF Data SDM-2020 - Manual (Page 161)

SDM-2020 Satellite Demodulator Revision 4
ECL/HSSI Data Interface MN/SDM2020D.IOM
10–9
10.1.4.3 Terrestrial Extended Signal Definitions
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 will be routed to RESERVED (from
DCE) HSSI pins. Refer to Table 10-5 for definition of signals.
Table 10-5. Definition of Signals
Signal Definition
Transmitter Synchronization Signal
(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.
10.1.4.4 Terrestrial Data Rate
The terrestrial interface supports synchronous data transfer rates from 1.5 to 70 Mbps.
Notes:
1. EIA-612 (Electrical Characteristics for an Interface at Data Signaling Rates
up to 52 Mbps) defines the electrical characteristics required for data
transfers up to 52 Mbps utilizing ECL driver/receiver technology.
2. The HSSI port will comply with EIA-612 for transfers less than 52 Mbps.
3. For short distances, an SCSI-2 cable will work, although the impedance will be
wrong.
The recommended cable is a CISCO “CAB-HSI1 (DTE to DCE)” or “CAB-HNUL
(DCE to DCE)” incorporating twisted, shielded pairs. The maximum cable length should
be
≤ 3 ft (7.62 cm) for the 70 Mbps transfer rates.