805U Radio Modem Module
User Manual
Page
22
©
November 2004
If repeater B is able to hear the original message from module X (on group address 2), then it
will re-transmit it on. But if it cannot, then the message will not be transmitted on to Z.
3.6
Controlled Mode
In controlled mode, data is only transferred between two modules (that is, a point to point
link). One of the modules is configured as a “master” unit and the other as a “slave” unit.
There can also be up to five intermediate repeaters in the link. Each 805U unit is configured
with a unit address - only the unit with an address matching the destination address of the
radio message will process the message and output the serial data.
To establish a link, the master will transmit a special “connect” message. This initial message
will not include any data. If the “slave” unit receives the initial message, and is not already
connected to another 805U unit, it will return an acknowledgment message. Both units will
activate their DCD LED, and also activate their DCD output signal. If the master unit does
not receive the acknowledgment, the DCD output will reset. When the connection is made
(DCD set), the 805U units can transmit data to each other.
Once the communications channel has been established, the 805U unit will accept input data
and send radio messages with data. When a 805U unit receives a radio message, it will check
the system address and destination address, and also the error-check (optional). If these are
correct, it will return a ACK (acknowledgment) message to the source unit. If these are
correct, it will return a ACK (acknowledgment) message to the source unit. If the system
address or destination address is not correct, or if the error-check is not correct, then no
return message is sent.
Establishing a Communications Link
Master Unit
Slave Unit
•
Listen to ensure channel is clear
•
If clear, transmit “connect”
message
•
Radio TX LED flashes
----------------->
•
Receives message
•
Radio RX LED flashes
•
Check system and destination
address
•
If OK, set DCD LED and
output
•
Radio RX LED flashes
<-----------------
•
If message OK, transmit back
an ACK message.
•
Radio TX LED flashes
•
Acknowledgment received okay
communication link established
•
Set DCD LED and output
