User's Manual

455U Radio Modem Module User Manual
Page 24 © November 2004
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
If the source unit does not receive an ACK message, it will re-transmit the same message. It
will attempt to transmit the message the configured number of times (S-Register S30). If the
unit still does not receive an ACK message after the configured number of attempts, it will
reset the LINK LED, and reset the DCD output on the DB9 RS232 port (AT&C) and reset the
DIO output if configured (AT#O).
During normal operation, if there has been no radio activity for a period (called the “link
check” period), the initiator will transmit a “check” message to check the radio path. The link
check period is a time configured by the user (S-Register S6). If the responder doesn’t receive
any messages within the configured link check timeout (AT\T), it will drop the radio link.
(Turn off the LINK LED, and reset the DIO and DCD signals if configured).
Successful Communications
Source Module Destination Module
• Serial data is received
• Serial LED flashes
• Listen to ensure channel is clear
• If clear, transmit message
• Radio TX LED flashes
----------------->
• Receive message
• Radio RX LED flashes
• Check system and destination
address
• If OK, check error-check
• Radio RX LED flashes
<-----------------
• If message okay, transmit back
an ACK message.
• Radio TX LED flashes
• Acknowledgment received okay
- communication complete
• Serial data is output
• Serial LED flashes