805U Radio Modem Module
User Manual
Page
26
©
November 2004
Repeater Communications
Successful
Unit A
Source
•
Transmit
message
Receive ACK
--->
<---
Unit B
Repeater
•
Receive
message
•
Re-transmit
message
•
Receive ACK
•
Re-transmit
ACK
--->
<---
Unit C
Repeater
•
Receive
message
•
Re-transmit
message
•
Receive ACK
•
Re-transmit
ACK
--->
<---
Unit D
Destination
•
Receive
message
•
Transmit
ACK
•
Output data
Repeater units may also act as destination addresses for some transmissions and output data
to a host device.
3.7
What Operating Mode to Use ?
3.7.1
Transparent or Controlled Mode?
Transparent mode provides simpler operation as the units do not acknowledge transmissions
received. However reliable operation in transparent mode will only occur if the host devices
check the messages and return acknowledgments. Generally, if a device is able to operate on a
RS485 multi-drop serial link, it is suitable for transparent mode.
Controlled mode is suitable for point-to-point links. For multi-point networks, a “master” host
device must control connecting and disconnecting to remote units.
It is possible to configure different units in the same system with different operating modes,
however the system will not operate. A 805U unit configured in one mode will not process a
message received from a unit in the alternate mode.
3.7.2
Error Check ?
Error-checking may be configured in both transparent and controlled mode. When the error-
check is configured, two additional bytes are attached to the end of each message. These bytes
are used to detect any corruption of the data when it is received at another 805U unit.
When a unit with error-check configured receives a radio message, it will not output data until
it has received the whole message and ensures that the error-check is correct. If the unit does
not have error-check configured, then it will output data as it is received. Hence operation of
the units is faster if error-check is not configured.
We recommend that units in the same system have the same error-check configuration,
however it is possible for users to configure the units differently. If a unit without error-check
configured receives a message which includes an error-check, then the unit will treat the
additional two bytes as data and output them to the host device. If a unit with error-check
