Comtech EF Data DD240XR Rev Е - Manual (Page 52)

User Interfaces DD240XR High-Speed Digital Demodulator
4-32 MN-DD240XR – Rev. E
respond to the override simultaneously with different information, or asynchronously in their
respective message packets and response packets, causing a collision on the serial control bus.
To preclude control bus data contention, different IDs must always be assigned to the equipment.
If two or more devices are configured for direct-linked operation, then the M&C computer and all
other devices configured in the same manner must be programmed to inhibit broadcast of the
corresponding multi-drop override ID.
The multi-drop override ID is always accepted by devices of the same type on a common control
bus, independent of the actual DESTINATION ID. These Override IDs with the exception of
“BROADCAST” are responded to by all directly linked devices of the same type causing
contention on the bus. The “BROADCAST” ID, on the other hand, is accepted by all equipment
but none of them returns a response packet to the remote M&C.
The following multi-drop override IDs are device-type specific, with the exception of
"BROADCAST". These are summarized below with ID values expressed in decimal notation:
Note that multi-drop override ID 01 can be used interchangeably to broadcast a message to a
DMD-3000/4000 modem, a DMD-4500/5000, a DMD15 modem, or a DVB3030. Radyne
Corporation recommends that the multi-drop override IDs be issued only during system
configuration as a bus test tool by experienced programmers, and that they not be included in run-
time software. It is also advantageous to consider the use of multiple bus systems where
warranted by a moderate to large equipment complement.
Therefore, if a DMD15 Modulator is queried for its equipment type identifier, it will return a "20"
and DMD15 Demodulator will return a "21". A DMD15 Modem will also return a "22". A DVB3030
Video Modulator will return a “23.”
4.3.6 Software Compatibility
The COMMSPEC, operating in conjunction within the RLLP shell, provides for full forward and
backward software compatibility independent of the software version in use. New features are
appended to the end of the DATA field without OPCODE changes. Older software simply
discards the data as extraneous information without functional impairment for backward
compatibility.
If new device-resident or M&C software receives a message related to an old software
version, new information and processes are not damaged or affected by the omission of data.
The implementation of forward and backward software compatibility often, but not always,
requires the addition of new Opcodes. Each new function requires a new Opcode assignment if
forward and backward compatibility cannot be attained by other means.
Table 4-3. Broadcast lDs
Directly-Addressed Equipment Multi-Drop Override ID
Broadcast (all directly-linked devices) 00
DMD-3000/4000, 4500 or 5000 Mod Section, DMD15 01
DMD-3000/4000, 4500 or 5000 Demod Section, DMD15 02
RCU-340 1:1 Switch 03
RCS-780 1:N Switch 04
RMUX-340 Cross-Connect Multiplexer 05