Chapter Three
Operation
Man_805U Rev 1.8
Page
23
If the source unit does not receive an ACK message, it will re-transmit the same message. It
will attempt to transmit the message up to five times. If the unit still does not receive an
ACK message after five attempts, it will reset the DCD LED, and reset the DCD output.
During normal operation, if there has been no radio activity for a period (called the “link
check” period), the “master” unit will transmit the “connect” message to check the radio
path. The link check period is a time configured by the user.
Successful Communications
Source Module
Destination Module
•
Serial data is received
•
Serial RX 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 TX 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 up to four times
----------------->
•
If no ACK message received
after five attempts
•
“NO CARRIER” message sent
to host
•
DCD signal and DCD LED reset
The time taken to transmit a message is :-
|------------HEADER-------------|--------------------DATA-----------|-----------|
lead-in
system unit repeater dest. zero
data
error check
10msec
address addr addrs's addr byte
No. of bytes
2
1 0 - 5 1
1
no. of data bytes
2
The time for each byte is 0.5msec @19200 bits/sec. If error checking is not configured at the
receiving unit, data will start to be output approx 1msec after the "zero" byte has been
