Comtech EF Data CDS-100 - Manual (Page 25)

CDS-100 Diversity Switch MN-CDS100
Introduction Revision 1
1–5
1.3 Functional Description
The CDS-100 Diversity Switch module does NOT perform any IF or Data switching. Rather, the
CDS-100 monitors the status of each modem and monitors the external control interface to
determine if it needs to force the Online modem to Offline (and Offline to Online).
1.3.1 Switch / Modem Operation
The CDS-100 is configured with two modems, RF equipment, and antenna to form a complete
‘Chain Redundant’ communication system. A diversity controller within the CDS-100
continuously monitors the status of faults for both modems to determine which modem should
be Online and Offline.
The control cable connection between the modems and the CDS-100 (using the ‘J3 | Control A’
and ‘J4 | Control B’ DB-9F female connectors) includes four signal groups:
• First, serial full-duplex communication lines are routed from one modem to the other
modem via the CDS-100. Using these lines, this Online unit can query the Offline unit at
regular intervals to determine its configuration. If a difference in configuration is detected,
the Online unit will reconfigure the Offline unit so that the configurations are always
synchronized. This process is entirely automatic – if the Offline unit is replaced, it does not
have to be manually reprogrammed to match the Online unit.
• Second, the Modem’s Unit, Tx and Rx faults signals from both modems are routed to the
CDS-100. This allows the diversity controller to always know the health status of both
modems.
• Third, the online/offline signals are routed from the CDS-100 to each modem. Based on the
modem faults, the CDS-100 will determine which modem should be Online and Offline. In
the event that both modems indicate faults through some malfunction, the CDS-100 switch
will select, by default, Modem ‘A’.
• Fourth, +12V is routed from each modem to the CDS-100 for operational power. This power
from both modems is diode OR’d so that the switch remains active if power is lost from one
of the modems.
The CDS-100 provides two DB-9M male connectors – ‘J1 | Ext Fault Input A’ and ‘J2 | Ext Fault
Input B’ – to allow connection to any electrically compatible external controller. The CDS-100
provides multiple electrical interfaces in support of a variety of user implementations. You may
use these connections to manually switch which modem is Online, by using an external input
provided by the external controller. To activate the CDS-100’s external ports, you must set the
‘Unit+EXT’ DIP switch to ON. When the External Port DIP switch is in the OFF position, the CDS-
100 works identically to the CRS-180 1:1 redundancy switch, but without the RF switching.
Each external port has three control lines: two lines are active LOW and one line is active HIGH.
Only one line per External Port may be used at a time. Minimum pulse width for a valid signal is