User's Manual

455U-D Radio Modem Module User Manual
Page 12 © Jan 2008
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 and reset the DIO
output (if configured).
During normal operation, if there has been no radio activity for a period (called the “link
check” period), the master unit will transmit a “check” message to check the radio path. The
link check period is user-configurable (S-Register S6). If the slave doesn’t receive any
messages within the configured link check timeout (Configuration Setting \T), it will drop the
radio link, and 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
Unsuccessful Communications
Source Module Destination Module
• Listen to ensure channel is clear
• If clear, transmit message
• TX LED flashes
----------------->
• Receives message
• RX LED flashes
• Check system and destination
address
• If incorrect, transmit no message
and no serial output.
• No ACK received
• Retry multiple times (Configure With
S-Register S30)
----------------->
• If no ACK message received after
all attempts
• “NO CARRIER” message sent to
host
• DCD signal and DCD LED reset