User's Manual

FreeWave Technologies Spread Spectrum Transceiver User Manual
900 MHz and 2.4 GHz
V5.0S
15
(2) Max Slave Retry
(3) Retry Odds
While packets transmitted from the master to the slaves in a Multipoint network
are not acknowledged, packets transmitted from slaves to the master are.
However, it is possible that more than one slave will attempt to transmit to the
master at the same time, and it is therefore important that a protocol exists to
resolve contention for the master between slaves. This is addressed through
parameters (2) Max Slave Retry and (3) Retry Odds. The Max Slave Retry setting
defines how many times (0 to 9) the slave will attempt to retransmit a packet to the
master before beginning to use a back-off algorithm. Once the slave has
unsuccessfully attempted to transmit the packet the number of times specified in
Max Slave Retry it will attempt to transmit to the master on a random basis. The
Retry Odds parameter determines the probability that the slave will attempt to
retransmit the packet to the master; a low setting will assign low odds to the slave
attempting to transmit and conversely a high setting will assign high odds. An
example of how this parameter might be used would be when considering two
different slaves in a Multipoint network, one close in with a strong RF link and the
other far from the master with a weak link. It may be desirable to assign a higher
Retry Odd to the slave with the weaker link to give it a better chance of competing
with the closer slave for the master's attention.
When Retry Odds = 0 the slave will try to talk to the master the number of times
specified in the Max Slave Retry parameter. If it is unsuccessful the slave will
flash (purge) its RS232 input buffer.
(4) DTR Connect
Another parameter in a Multipoint network is (4) DTR Connect. When set at 1 the
slave will connect to the master if it is free when the DTR line goes high on the 9
pin RS232 connector. In setting 2 the transceiver will accumulate data in its buffer
and transmit in a burst when the buffer is full. This mode is valuable when a
network has many low data rate devices and it is desirable to increase overall
network capacity. In setting 0 the transceiver will transmit when RS232 data is
received.
(5) Repeater Frequency
The repeater's hopping pattern must also be set in a Multipoint network; this is
accomplished with parameter (5) Repeater Frequency. Setting this parameter is in
contrast with point-to-point mode where the repeater automatically uses the
master's hopping pattern. The repeater may be programmed to either use the
master's hopping pattern (selection 0) or its own (selection 1).
Please refer to the Application Note on the wwww.freewave.com website.