User's Manual

6 MHX-900 Operating Manual: Chapter 2 Initial Setup and Configuration
Warning: Using an antenna that
is inappropriate for use with the
MHX-900 module could result in
undesired performance, and may
damage the unit. It is the user’s
responsibility to ensure the
antenna has adequate lightning
protection.
B. Point-to-Multipoint
To establish a point-to-multipoint network, the following requisites must be
satisfied:
n The Operating Mode for one modem must be configured as a
Point-to-Multipoint Master, and the others as Point-to-
Multipoint Slaves.
n The Wireless Link Rate for all modems must be the same.
n The Network Address assigned to all modems must be the same.
n Each Slave must be assigned a unique Unit Address (Unit Address
0 is not supported).
n The same Hopping Pattern must be selected for all modems.
n The Hopping Interval is determined by the Master modem, and is
therefore configured only at the Master.
n All modems must use the same Encryption Key.
Each of the parameters above are defined by specific S registers. Settings are
not immediately stored in non-volatile memory. The command &W writes
the current configuration into non-volatile memory, and are therefore retained
even after powering down. Each item and the settable parameters within the
modem configuration are described in detail in Chapter 3: Configuration
Options.
2.4 Checking the Link
Once configured properly, a pair or set of communicating modems can be tested
to ensure that a link can be successfully established. Connect an appropriate
antenna to each MHX-900 module. The modems should indicate the status of
the wireless link via the RSSI outputs on each unit:
If the link is good, up to three RSSI outputs should be active; and if the link
is absent (due to a fault at one end or another, such as misconfiguration), the
outputs will be inactive.
It is recommended that if MHX-900 modules will be deployed in a field
where large distances separate the units, the modems should be configured
and tested in close proximity (e.g., in the same room) first to ensure a good
link can be established and settings are correct. This will facilitate
troubleshooting, should problems arise. In a multipoint system, only the
Slave modems give valid RSSI readings.
Microhard Systems Inc. provides a development system which supplies all
system power and RS-232 level shifting circuits required to connect a MHX-
900 module to a PC. This can serve as an invaluable aid in OEM system
design.