Comtech EF Data DD2401 - Manual (Page 31)

DD2401 Satellite Demodulator User Interfaces
MN-DD2401 - Rev. G 4- 7
4.4 Remote Port User Interface
The Remote Port of the DD2401/DD2401L allows for complete control and monitor functions via
an RS-485 or RS-232 Internal Dip Switch Configurable Serial Interface.
Control and status messages are conveyed between the DD2401/DD2401L and the subsidiary
modems and the host computer using packetized message blocks in accordance with a
proprietary communications specification. This communication is handled by the Radyne Link
Level Protocol (RLLP), which serves as a protocol ‘wrapper’ for the M&C data.
Complete information on monitor and control software is contained in the following sections.
4.4.1 Protocol Structure
The Communications Specification (COMMSPEC) defines the interaction of computer resident
Monitor and Control software used in satellite earth station equipment such as Modems,
Redundancy Switches, Multiplexers, and other ancillary support gear. Communication is bi-
directional, and is normally established on one or more full-duplex 9600-baud multi-drop control
buses that conform to EIA Standard RS-485. If a single device is placed on a single control bus,
then the control bus may conform to EIA Standard RS-232.
Each piece of earth station equipment on a control bus has a unique physical address, which is
assigned during station setup/configuration or prior to shipment. Valid decimal addresses on one
control bus range from 032 to 255 for a total of up to 224 devices per bus. Address 255 of each
control bus is usually reserved for the M&C computer.
4.4.2 Protocol Wrapper
The Radyne COMMSPEC is byte-oriented, with the Least Significant Bit (LSB) issued first. Each
data byte is conveyed as mark/space information with one mark comprising the stop data. When
the last byte of data is transmitted, a hold comprises one steady mark (the last stop bit). To begin
or resume data transfer, a space (00h) substitutes this mark. This handling scheme is controlled
by the hardware and is transparent to the user. A pictorial representation of the data and its
surrounding overhead may be shown as follows:
S1 S2 B 0 B 1 B 2 B 3 B 4 B 5 B 6 B 7 S1 S2, etc.
The stop bit, S1 is a mark. Data flow remains in a hold mode until S1 is replaced by a space. If S1
is followed by a space, the space character is considered a start (ST) and not part of the actual
data (B
0
- B
7
).
The above byte-oriented protocol is standard for UART based serial communication ports such as
Workstation or Personal Computer (PC) COM ports. COM ports should be configured for 8 data
bits, no parity, and one stop bit. For example, for 9600-baud operation, COM ports should be
configured as:
9600, 8, N, 1
The COMMSPEC developed for use with the Radyne Link Level Protocol (RLLP) organizes the
actual monitor and control data within a shell, or ‘protocol wrapper’, that surrounds the data. The
format and structure of the COMMSPEC message exchanges are described herein. Decimal
numbers have no suffix; hexadecimal numbers end with a lower case h suffix and binary values