User`s guide

Broadcast Multidrop
This mode of operation is determined by the configuration command keyword
ptpmode being set to OFF. Broadcast multidrop mode provides a mechanism for
building very large networks using the RMX232 radio modem combined with intelligent
host controllers.
In broadcast multidrop mode, the radio mode does not implement network layer
functionality related to data packet routing, acknowledgement and retries. It merely
provides an error free mechanism for transferring data between multiple nodes.
The connected host device should provide network layer functionality. This
functionality includes such network features as node address encoding/decoding and
error detection/recovery mechanisms.
When in this mode of operation, the radio modem upon receiving serial data,
packetises the data and broadcast the packet. This packetised data is received by all
other radio modems within radio range, unpacketised (decoded) and sent to their
connected host device. The radio modem itself does not provided data packet
acknowledgements or timeout functions as associated with the reliable point-to-point
link operating mode.
The host devices must add appropriate protocol information, for data packetising,
addressing, error detection and acknowledgement, to the data that is to be broadcast
over the network. This protocol information is used by the receiving host to intelligently
decide if the data is for it, then either send a reply or just acknowledge receipt of the
data.
The site code and unit address is still used by the radio modem when working in
broadcast multidrop mode. For a given multipoint network all radio modems within a
group must contain the same site code and unit address.
MultiMaster Mode
This mode of operation is determined by the configuration command keyword
ptpmode being set to mmaster. This mode of operation enables multiple remote
modems, with ptpmode set to ON, to establish a connection with the master device.
The master will accept a connection request from a remote device of any unit address
but only for the specific site address as assigned in the master unit. Thus a maximum
of 15 remote modems are allowed to establish a connection with the master.
If the master modem is currently in connection with a remote modem, another remote
modem is prevented from establishing a connection to the master. Only once the
connection between the communicating pair has timed out (ctime timeout value) can
another connection be established.
When operating in this mode, it is advisable to keep data transfer sessions as short as
possible. Use the setting of ctime (on all modems) to ensure the link to a remote unit
is dropped quickly after a transfer is complete.
Upon a connection request coming into the master unit (on which mmaster is set), the
master unit changes its current unit address to reflect that of the remote modem, and
hence talk only with the remote modem. It is advisable to set the unit address of the
master unit to 0. The slave units can then be assigned a unit address between 1 and
15. The site address should be the same between all modems within the group.
User’s Guide Modem Operation Explained 4-8