Comtech-ef-data RCS20 Manual do Utilizador descarregar pdf (Página 149)

RCS20 M:N Redundancy Switch Revision 15

Remote Operations MN-RCS20 and CD-RCS20

A–7

pitfall, which is often overlooked, concerns multi-drop override IDs. All too often, multiple devices of the

same type are assigned in a direct-linked ("single-thread") configuration accessible to the M&C computer

directly. For example, if two DMD15 Modems with different addresses (DESTINATION IDs) are linked to

the same control bus at the same hierarchical level, both will attempt to respond to the M&C computer

when the computer generates a multi-drop override ID of 22. If their actual setup parameters, status, or

internal timing differs, they will both attempt to 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 in Table A-4 below with ID values expressed in decimal notation:

Table A-4. 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

CDS-780 Clock Distribution System 06

SOM-340 Second Order Multiplexer 07

DMD-4500/5000 Modulator Section 08

DMD-4500/5000 Demodulator Section 09

RCU-5000 M:N Switch 10

DMD15 Modulator 20

1 2 ... 144 145 146 147 148 149 150 151 152 153 154 ... 201 202

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