Comtech EF Data OM20 - Manual (Page 41)

OM20 Universal Outdoor Modem OM20 Theory of Operation
MN-OM20– Revision 5 4–3
4.1.2 OM20 Baseband Processing Printed Circuit Card
The advent of million-plus gate count FPGAs, advanced logic synthesis tools, and DSPs
providing hundreds of MIPs enabled the design of a software configurable modem. Large, fast
FPGAs now provide designers with what is essentially an on the fly programmable ASIC. High
speed, complex digital logic functions that previously could only be implemented in dedicated
integrated circuits are now downloaded from a micro-controller through a serial or peripheral
interface. When a new digital logic function is needed, a new configuration file is loaded into the
FPGA. There is no limit to the number of digital logic configurations available to the FPGA,
aside from the amount of Flash memory available to the system microprocessor for storage of
configuration files.
The OM20 Baseband Processing Printed Circuit Card provides a flexible architecture that allows
many different modes of terrestrial and satellite framing, various FEC options, digital voice
processing, and several different modulation/demodulation formats. Also included on the
Baseband Printed Circuit Card are three synchronous interfaces on a 25-pin interface supporting
RS-422, V.35, and RS-232 data. All three interfaces are provided on the same connector (J3),
and are selectable from the terminal or Ethernet ports. Additionally, data may be passed through
the Ethernet port (J4). Ensure that the correct interface is selected in the unit prior to connecting
to the data interface. Refer to
Section 4 for further information on the data interface selection
parameters and programming.
The Baseband Printed Circuit Card also contains the Monitor and Control (M&C) Circuitry
responsible for:
 Programmable part setup and initialization
 Continuous control and adjustment of some functions
 Calibration
 Monitoring fault status
 Calculating and displaying measurements
 Calculations
 User monitor and control interface including front panel and remote
 Unit’s configuration and feature set
The M&C System is based on a powerful microprocessor with a large amount of Flash memory.
Several bus architectures are used to interconnect the M&C to all components of the OM20.
Communications to the outside world is done via connections to the remote/terminal/alarm port
(J2), or the Ethernet port (J4), and alarm ports. The M&C runs off of software programmed into
its Flash memory. The memory can be reprogrammed via the Ethernet port to facilitate changes
in software.