SEM910
If the application has more slave devices, or if it is desirable to increase the throughputs of the
slaves at the expense of the master SEM, contact Cirronet technical support for more details.
Co-located Networks
The radio architecture in the SEM allows multiple networks to be located in the same area
without interfering with each other. Depending on the scenario, either the network and/or the
sync commands are used to distinguish between networks of SEMs and to prevent interference
between the SEM networks.
If the master SEMs are not located close to each other (< 30 feet or 10 meters), simply assigning
different network numbers to the various networks of SEMs will allow the networks to co-exist
without interference. The network number selects one of 36 different hopping patterns, where the
hopping pattern is the pseudo-random sequence of frequencies over which the SEMs hop.
Because the different networks are using different sequences they will transmit on the same
frequency at the same time only rarely. These infrequent collisions are sufficient to reduce the
throughput in any meaningful way.
If the master SEMs are to be located close together, the SEMs allow the masters to be
synchronized as to when they send to slaves and when they receive from slaves. This
synchronization is allowed by the FCC in the United States. The FCC does not allow
synchronizing of the hop sequences to avoid all collisions. The SEM accomplishes the
send/receive synchronization through use of the Sync ports. The Sync ports of the SEM masters
are connected using standard RJ-11 cables. There is a Sync In and a Sync Out port to allow
daisy-chaining of SEM masters. One of the SEM masters is designated the Sync Master using the
sync master
command. Synchronization is enabled in the Sync Master and all connected master
SEMs using the
sync enable
command. The
sync wire
command must be issued to turn on
the Sync ports. Refer to the
Radio Commands
section for details.
Note: When synchronization is used in the United States, the hop fcc parameter must be left
enabled. Disabling this parameter will violate FCC rules governing spread spectrum radios.
©
2000- 2004 Cirronet
™
Inc
20
M-910-0003 Rev -
