Comtech EF Data DMD1050 - Manual (Page 30)

DMD1050 Satellite Modem Board Theory of Operation
MN-DMD1050 3–4
Revision 9
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 DMD1050.
Communication to the outside world is done via connections to the remote port, terminal port,
Ethernet port, and alarm ports. The M&C runs off software programmed into its Flash memory.
The memory can be reprogrammed via the Ethernet port to facilitate changes in software.
3.2 DMD1050 Functional Block Diagram
Figure 3-4 represents the DMD1050 Functional Blocks. The modem is shown in a typical
application with customer data, Tx/Rx RF equipment and an antenna.
3.2.1 Baseband Processing
The Baseband Processor performs all of the functions required for an IBS/IDR Framing Unit, a
Reed-Solomon Codec. In addition, the Baseband Processing Section provides for transmit clock
selection and rate adaptation as well as a rate adapter and Plesiochronous/Doppler (PD) Buffer in
the receive direction. A multiplexer is also provided for the SCT Clock Source for Loop Timing
Applications. The transmit and receive paths may be configured independently under processor
control.
3.2.2 Tx Baseband Processing
The Tx Data and Clock enters the Baseband Processor, passes through a Rate Adapting FIFO and
enters the Framer Processor. In Closed-Net Mode, the data passes through the framer unaltered.
In IDR & IBS framining enabled, it adds the appropriate framing as defined in IESS-308 and
309. The data is then sent to the Reed-Solomon Encoder.
The Reed-Solomon Encoder, encodes the data into Reed-Solomon Blocks. The blocks are then
interleaved and synchronized to the frame pattern as defined by the selected specification (IESS-
308, IESS-309, DVB, etc.). After Reed-Solomon Encoding, the composite data and clock are
applied to the BB Loopback Circuit.
The DMD1050 supports IBS & IDR compatible framing modes. Since
the modem does not have all supporting interfaces as stipulated by
IESS308/309, it is not 100% compliant. IBS and IDR framing modes are
supported in a Closed network Mode.
IMPORTANT