User's Manual
Table Of Contents
- FreeWave Technologies
- LRS-455-EU
- Data Transceiver
- Version 1.0, Revision A
- About FreeWave Transceivers
- Choosing a Location for the Transceivers
- Quick Start on a Point-to-Point Network
- Setting up a Transceiver
- Operation Mode
- Baud Rate
- Modbus RTU Timing
- The Modbus RTU setting causes the radio to wait for an amount of time, “gathering” data before sending out the radio link.
- With a setting of 0 (Disabled), the radio will send data out its radio link as soon as the data is received into the serial port.
- With a setting of 1, the radio will wait for a number of slots equal to 2 times the Master Packet Repeat setting before sending the received data out the radio link. For example, if Master Packet Repeat = 3, the radio will wait for 6 slots, gathering ...
- With a setting of 2 and higher, the radio will wait for a number of slots calculated by the following formula:
- (Modbus RTU Setting + Master Packet Repeat Setting + 1) x 2
- For example, in a radio where the Modbus RTU setting = 2 and the Master Packet Repeat setting = 3, the radio will wait for (2+3+1) x 2, or 12 slots.
- Call Book
- Radio Transmission Characteristics
- Edit Radio Transmission Characteristics
- MultiPoint Parameters
- Edit MultiPoint Parameters
- Radio Information
- Operational RS-422 and RS-485 Information
- RS232 Pin Assignments
- RF Board Pinout
- FreeWave Technical Support
- Errata
LRS-455-EU Data Transceiver Users Manual
LUM0032AA Rev A Version 1.0 2
Choosing Point-to-Point or Point-to-MultiPoint Operation
A Point-to-Point network is limited to one Master and one Slave transceiver.
In a Point-to-MultiPoint network (also referred to as MultiPoint network) the transceiver, designated as a
Master, is able to simultaneously communicate with numerous Slaves. In its simplest form, a MultiPoint
network functions with the Master broadcasting its messages to all Slaves and the Slaves responding to
the Master when given data by the device connected to the data port.
It is important to note the differences between Point-to-Point and MultiPoint networks. In a Point-to-Point
network all packets are acknowledged, whether sent from the Master to the Slave or from the Slave to the
Master. In a MultiPoint network, outbound packets from the Master to Slaves are sent a set number of
times determined by the user. The receiving transceiver will accept the first packet received that passes
the 32 bit CRC. However, the packet is not acknowledged. On the return trip to the Master, all packets
sent by the Slave are acknowledged or retransmitted until they are acknowledged. Therefore, the return
link in a MultiPoint network is generally very robust.
Note: In licensed band operation it is suggested to set the repeated master packets at 0 due to
the spectrum being quiet. This will maximize throughput and leverage the advantages of licensed
band operation.
Traditionally, a MultiPoint network is used in applications where data is collected from many instruments
and reported back to one central site. As such, the architecture of such a network is different from Point-
to-Point applications. The number of radios in a MultiPoint network is influenced by the following
parameters:
1. Size of the blocks of data. The longer the data blocks, the smaller the network capacity.
2. Baud rate.
3. The amount of contention between Slaves. Polled Slaves vs. timed Slaves.
For example, if the network will be polling Slaves once a day to retrieve sparse data, several hundred
Slaves could be configured to a single Master. However, if each Slave will be transmitting data at greater
levels, then fewer Slaves should be linked to the Master. The overall network will be closer to capacity
with fewer Slaves.
For examples and additional information on data communication links, see the section Examples
of Data Communication Links later in this document.