DNT500
2008 by RF Monolithics,
Inc.
4
M-0500-0000 Rev D
2. DNT500 RADIO OPERATION
2.1 Network Synchronization and Registration
As discussed above, frequency hopping radios such as the DNT500 periodically change
the frequency at which they transmit. In order for the other radios in the network to re-
ceive the transmission, they must be listening to the frequency over which the current
transmission is being sent. To do this, all the radios in the network must be synchronized
and must be set to the same hopping pattern.
In point-to-point or point-to-multipoint networks, one radio module is designated as the
base station. All other radios are designated remotes. One of the responsibilities of the
base station is to transmit a synchronization signal to the remotes to allow them to syn-
chronize with the base station. Since the remotes know the hopping pattern, once they are
synchronized with the base station, they know which frequency to hop to and when.
Every time the base station hops to a different frequency, it immediately transmits a syn-
chronizing signal.
When a remote is powered on, it rapidly scans the frequency band for the synchronizing
signal. Since the base station is transmitting up to 50 frequencies and the remote is scan-
ning up to 50 frequencies, it can take several seconds for a remote to synchronize with
the base station.
Once a remote has synchronized with the base station, it will request registration informa-
tion to allow it to join the network. Registration can be handled automatically by the base
station, or it can be controlled by allowing the base station host application to authenti-
cate the remote for registration. When a remote is registered, it receives several network
parameters from the base station, including HopDuration, Nwk_ID, FrequencyBand and
Nwk_Key (see Section 5.2 for parameter details). Note that if a registration parameter is
changed at the base station, it will update the parameter in the remotes over the air.
Among other things, registration allows the tracking of remotes entering and leaving a
network, up to a limit of 255 remotes. The base station builds a table of serial numbers of
registered remotes using their three-byte serial numbers (MAC addresses). To detect if a
remote has gone offline or out of range, the registration is “leased” must be “renewed”
once every 250 hops. Any transmission from a remote running on a leased registration
will renew its lease with the base station.
2.2 Transparent and Protocol Serial Port Modes
DNT500 radios can work in two serial port data modes: transparent and packet protocol.
Transparent formatting is simply the raw user data. Packet protocol formatting uses a
framing character, length byte, addressing, command bytes, etc. Transparent mode opera-
tion is especially useful in point-to-point systems that act as simple cable replacements.
In point-to-multipoint systems where the base station needs to send data specifically to
each remote, protocol formatting must be used. Protocol formatting is also required for
configuration commands and responses, and sensor I/O commands and responses. Proto-
col formatting details are covered in Section 5.