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14 Pelco Manual C546M (8/98)
4.0 GUIDELINES FOR PORT EXPANDER USE
The following points are listed as Pelco recommended guidelines for port expander
use. The reason the port expander exists at all is to extend the current port limit past
that physically allowed by the CM9760-CC1. Even though, the 32 port limit imposed
by the CC1 is usually sufficient for most system configurations, the advent of
extremely large system configurations made the port expander a necessity. That
being said, the guidelines are as follows:
1. Do not use a port expander until all or as many as possible of the available
sercom ports on the CC1 are used.
2. If it becomes necessary to use a port expander, use the port expander to hook
up those pieces of equipment that you have the largest number of.
3. If you have several different equipment types, all of which are candidates for
connection to a port expander, then the following – in order of hook-up
preference – is recommended by Pelco:
a. Receiver/drivers
b. Multiplexers (if necessary)
c. Keyboards
One should not hesitate to use the port expander to extend port density when more
receiver/drivers need to be introduced for system expansion, for this is the primary
reason the port expander was created.
One should be less hesitant to attach multiplexers and keyboards as indicated in
the “order of preference” hook-up in step 3 above. In particular, one should avoid
attaching addressable multiplexers (those capable of being daisy-chained) to a port
expander. Not that it could not be done, but that it would be a waste of resources.
For keyboards, special programming considerations are required. If you can’t avoid
using the port expander to attach keyboards, then follow the detailed programming
instructions contained in the CM9760-MGR manual.