Operation
RFI-9256 Radio Modem User Manual
Page 23 of 109
5.2 Radio Operation
5.2.1 Overview of Operation
The RFI-9256 is a time division duplex / frequency division duplex (TDD/FDD) frequency hopping spread
spectrum (FHSS) radio. The RFI-9256 divides its transmission up into frames, where each frame contains
communication between two radios on a fixed channel and lasts for a fixed period of time.
The RFI-9256 is a master / slave based system. In any one radio network there is a single master and
multiple slaves. The master may send messages to any slave, but the slaves may only send messages to the
master. It is the responsibility of the master to synchronise all the slaves, and to allocate time for slaves to
transmit.
The framing arrangement is shown in Figure 7.
Frame 1
f
1
Frame 2
f
2
Frame 3
f
3
Frame 4
f
4
Frame 5
f
5
Frame 6
f
6
Frame Time
20ms
Master
Packet
Slave
Packet
Figure 7: RFI-9256 time division duplex / frequency division duplex (TDD/FDD) operation
Each frame occurs on a different frequency and lasts for a fixed period of time, 20ms in the above diagram.
This is referred to as the channel dwell time or the frame time. The RFI-9256 supports configurable frame
times between 5 and 35ms. The selection of frequencies is based on a pseudo-random hopping sequence,
with 32 user selectable hopping sequences.
Each frame can be used to transmit up to two packets, the master packet and the slave packet. In the master
packet the master sends control data, followed by user payload that is destined for either one slave, or
broadcast to all slaves. In the slave packet a slave will transmit control data followed by a user payload
destined for the master.
