User manual

905U-D Radio Modem User Manual
Man_905D_1.10.doc Page 28
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 905U-D 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 905U-D 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.