User`s guide

Radio Modem Addressing Scheme
The RMX232 radio modem provides a two tier addressing scheme applied to each
outgoing packet of data. Seven data bits are used by the radio modem for data packet
addressing, these being divided into a 3 bit site code (8 possible sites) and a 4 bit unit
address (16 possible unit pairs).
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Unit Addr. 4 bit Site Code. 3 Bit N/A
Point-to-Point Addressing: Site/Unit
Point-to-Multipoint Addressing: 0 - 127.
Addressing Scheme:
N/A Address: 7 Bit
In its most basic form the site code and unit address combined allow up to 127 unique
point-to-point link paths. That is to say that up to 127 point-to-point links may operate
successfully (but not necessarily at maximum through put rate) within close radio
proximity to one another.
The main purpose of offering an addressing scheme consisting of site codes and unit
addresses is to provide logical isolation for groups of up to 16 radio modem pairs plus
repeaters. This is useful when a number of operating sites, in close proximity, may use
radio modem pairs and repeaters but need to remain logically separate.
A repeater will repeat only data packets matching its own site code, and reject all
others. Therefore a single repeater can be used to extend the operating range of up to
16 point-to-point links.
In order for a point-to-point link to be established between 2 radio modems, they each
must have matching site codes and unit addresses.
When used in a point-to-multipoint configuration, the unit address and site code is
combined using the addr command to provide up to 127 individually addressed slave
nodes.
The individual address of each slave device is made up from combining the unit and
site code. Use the following formula for deriving the address used by the addr
command to address a slave modem.
Address = (Site Code * 16) + Unit Address
For example:
Unit 4 @ Site 2 = (2 * 16) + 4 = 36
Hence use addr 36 to address the modem in point-to-multipoint mode
User’s Guide Modem Operation Explained 4-3