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RADIUS
Product
Description
PDR221
iom_pdr221_04_r02.doc
Rev 02
Page 19 (60)
7.8 Communication
The system distinguishes between direct slaves and
slaves via repeater
. A direct slave can only
receive data from, and transmit data to, the master in the system. A
slave via repeater
can only
receive data from, and transmit data to, the repeater in the system.
When the master transmits a telegram, this will be received by the slaves and the repeater (if a
system is so configured) at the same time. When the repeater has received the telegram, it will
retransmit it to the
slaves via repeater
. If then a
slave via repeater
answers the telegram, this is
sent to the repeater which in turn retransmits it to the master. If a direct slave answers, its telegram
is sent directly to the master.
In the system which contains
slave and repeater
, slaves and
slaves via repeater
, the direct slaves
must wait to answer until the repeater has transmitted the telegram. This is to avoid collisions. In a
slave with repeater delay
a time delay is automatically set which will delay the response
transmission to the Master until the repeater has repeated the message. The purpose of the delay
time is so that collisions on the radio channel will never occur.
A telegram sent by a
slave via repeater
never collides with the repeater’s telegram because of the
fact that the slave does not receive the telegram until the repeater has finished its transmission.
This is also the case when an direct
slave with
delay for repeater
answers.
Figure 4. Polling of slave via repeater
The repeater repeats the slave’s telegram
The repeater repeats the master’s telegram
The master transmits the telegram
The
slave via repeater
answers
Master
Repeater
Slave
Slave via repeater