User Manual

Global Transceiver Module (GXM) Wireless Data Transceiver User Manual
LUM0031AA
Version 1.0 33
The default setting of 0 disables this function, where as a setting of 1 enables RTS-CTS control.
RTS-CTS setting 2 is described in detail in the application note #5437 “DTR to CTS Line Alarm Feature”.
With an RTS to CTS setting of 1, the Master senses the RTS line prior to all scheduled packet
transmissions. If the state has changed, the Master will then transmit a message to the Slave with the
new status. This transmission will occur regardless of data being sent. If data is ready to be sent, the
RTS status message will be sent in addition to the data. In Point-to-Point mode, the Master will continue
sending the new status message until it receives an acknowledgment from the Slave. In MultiPoint mode,
the Master will repeat the message the number of times equal to the Master Packet Repeat value in the
MultiPoint Parameters menu.
Master transmit times are completely asynchronous to the occurrence of any change of the RTS line; the
latency time from RTS to CTS is variable. The Max and Min Packet Size parameters in the Radio
Parameter menu determine this duration. Setting both parameters to their maximum value of 9 will
produce a maximum latency time of approximately 21 ms, given no Repeaters in the network. At the
minimum settings for Max and Min Packet Size (0), the time will be approximately 5.9ms. Please note that
this latency can increase significantly if packets are lost between the Master and Slave. In Point-to-
MultiPoint mode, no absolute guarantee is made that the state change will be communicated to all
Slaves. In Multipoint networks with Repeaters present, the latency will be cumulative for each serial
Repeater.
For example: If the latency between the Master and the first Repeater is 15 ms, and 2 serial Repeaters
are present, the total latency will be 45 ms. (M—R1 (15 ms) + R1—R2 (15 ms) + R2—S (15 ms) = 45 ms)
Note: The RTS to CTS feature does not function in Point-to-Point networks that contain a Repeater. If
this feature is needed in such network, the mode should be changed to Point-to-MultiPoint.
Note: If DTRConnect is enabled and set to 2, the RTS to CTS feature will not work.
Note: If the DTRConnect is enabled and set to 1, RTS to CTS mode takes precedence over the
functionality of the CTS line on the Slave relating to the DTRConnect feature.
Note: The RTS to CTS option is only available in RS232 mode.
(8)
RETRY TIME OUT
The Retry Time Out parameter in a Slave or Repeater sets the delay the unit will wait before dropping the
connection to a Master or Repeater in MultiPoint mode. The factory default is set at the maximum of 255.
The maximum setting means that if 1 packet in 255 is sent successfully from the Master to the Slave or
Repeater, the link will be maintained. The minimum setting is 8. This allows a Slave or Repeater to drop a
connection if less than 1 in 8 consecutive packets is successfully received from the Master.
On the other hand, the function in the Master is effectively the same. With a setting of 255, the Master
will allow a Slave or Repeater to stay connected as long as 1 packet in 255 is successfully received at the
Master.
The Retry Time Out parameter is useful when a MultiPoint network has a roving Master or Slave(s). As
the link gets weaker, a lower setting will allow a poor link to break in search of a stronger one.
Note: Setting Retry Time Out to 20 is recommended in areas where several FreeWave networks exist.
This setting will allow Slaves and Repeaters to drop the connection if the link becomes too weak,
while at the same time prevent errant disconnects due to interference from neighboring networks.
While intended primarily for MultiPoint networks, the Retry Time Out parameter may also be modified in
Point-to-Point networks. However, the value in Point-to-Point mode should not be set to less than 151.
FreeWave T
echnologies, Inc.
1180 S Flatiron Ct Ste F
Boulder, CO 80501
[phone]