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760 Mhz Data Transceiver Users Manual 

LUM0000XX Rev A 

Version 1.0 

27 

times. Therefore, it is important to find the optimal mix between network robustness, throughput, and 
latency. In general, a setting of 2 to 3 will work well for most well designed networks. 

Note:  The Master Packet Repeat may be set to 0 if the user software is capable of, or requires 

acknowledgment. In this case if a packet sent by the Master and not received by the Slave, the 
user software will control the retries as needed. 

 

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 (defined by the Retry Odds setting). Slave 
retries will stop when an acknowledgement is received from the Master.

 

While packets transmitted from the Master to the Slaves in a MultiPoint network are not acknowledged, 
packets transmitted from Slaves to the Master are. It is possible, that more than one Slave will attempt to 
transmit to the Master at the same time. Therefore, it is 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. 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.  Conversely, a high setting 
will assign higher odds. An example of how this parameter might be used would be when considering two 
different Slaves in a MultiPoint network, one with a strong RF link and the other with a weak RF link to the 
Master. It may be desirable to assign higher Retry Odds to the Slave with the weaker link to give it a 
better chance of competing with the closer Slave(s) for the Master's attention. 

When Retry Odds = 0, after the Slave has exhausted the number of retries set in the Max Slave Retry 
parameter and still not gained the Master’s attention, the Slave’s data buffer will be purged.   

With the setting of 0 in the Slave, the transceiver will transmit when RS232 data is received.  A setting of 
1 will form a Point-to-Point link with the Master when the DTR line is high.  With a setting of 2, the 
transceiver will transmit in bursts.  This mode is valuable when a network has many low data rate devices 
and it is desirable to increase overall network capacity.  

Note:  If ‘DTRConnect’ is set to 1 and the ‘RTS to CTS’ function is enabled on the radio, then ‘RTS to 

CTS’ takes precedence over ‘DTRConnect’. 

Note:  If ‘DTRConnect’ is set to ‘2’ and ‘RTS to CTS’ is enabled, then ‘RTS to CTS’ is ignored. The 

transceiver has two separate transmit and receive user data buffers.  These buffers are 2 Kbytes 
each.  In case of a buffer overflow, the transceiver will output unpredictable data.  

 Repeaters are not available in the FreeWave 760 MHz Data Transceivers. 

Network ID allows MultiPoint networks to be established without using the Call Book.  The default setting 
of 255 enables the Call Book.  To enable Network ID the value must be set between 0 and 4095 
(excluding 255).  Since Network ID does not use serial numbers, MultiPoint Masters may be replaced 
without reprogramming all of the Slaves in the network.  Slaves will link with the first Master that it hears 
that has a matching Network ID.  The Network ID function should be used in conjunction with the Subnet 
ID feature (If necessary).