Comtech EF Data SDM-2020 - Manual (Page 130)

SDM-2020 Satellite Modulator Revision 7
ECL/HSSI TX MN/SDM2020M.IOM
10-9
10.1.4.4 T
ERRESTRIAL
D
ATA
R
ATE
The terrestrial interface supports synchronous data transfer rates from 1.5 to 70 Mbps.
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
using ECL driver/receiver technology.
The HSSI port complies with EIA-612 for transfers less than 52 Mbps.
For short distances, a SCSI-2 cable is satisfactory, although the impedance is in error.
The recommended cable is a computer-grade SCSI-2 cable incorporating twisted,
shielded pairs. The maximum cable length should be
≤ 3 ft (7.62 cm) for the 70 Mbps
transfer rates.
10.1.4.5 T
ERRESTRIAL
E
LECTRICAL
C
HARACTERISTICS
All signals are balanced, differentially-driven, and received at standard 10K/100K ECL
levels. Table 10-5 summarizes the electrical properties of the HSSI interface.
Table 10-5. HSSI General Specifications
General Specifications
Connectors 50-pin mini-D female for EIA-613 (HSSI) data.
Electrical Properties Per EIA-612 (10KH ECL).
TTL / TTL open-collector.
Typical Voltages Levels Differential voltage: ≥ 590 mV, 110Ω load
Input voltage range: -0.5 to -2.0V
Referenced to receiver common.
10.1.4.6 T
ERRESTRIAL
T
IMING
Refer to Figure 10-7 and Figure 10-8. The nominal interface timing is as follows:
• Clock is 50% duty cycle
• Data/control signals transition on the rising (low to high) edge of the clock
• Data/control signals are stable on the falling (high to low) edge of the clock
Terminal A “+” of the generator is positive with respect to Terminal B “-“ for a binary 1
or ON state. The B terminal of the generator is positive with respect to the A terminal for
a binary 0 or OFF state.