Westermo RD-48 - Manual (Page 25)

25 6153-2004
7.2 Selection of datarate / format
The data rate and format settings is used to decide the turning time on the RS-422/485
bus. For optimum performance the data rate and format settings needs to be set up
according to the used protocol.
The data rate switches selects the operating speed on both line-A and line-B. Observe
that the RD-48 is a transparent unit and the data rate needs to be the same on both
sides of the unit.
The format switches selects the data format on both line-A and line-B. 9,10 or 11-bit
format is used for asynchronous protocols. Synchronous mode activates the transmitter
for 11 bits after a detected edge in data. This mode is used for synchronous protocols.
7.3 Setting of retiming
Retiming is possible on higher data rates (187.5 kbit/s and higher) and recreates the
data bits to exact bit length set up by the speed selection. The use of retiming makes
it possible to connect an increased number of RD-48 units on a line.
7.4 Setting of anti-blocking
The anti blocking function secures transmission on each side of the RD-48 repeater.
If the line is constant active (blocked) for more than 50 ms the anti blocking function
will disconnect this side of the repeater. This makes it possible to communicate between
units on the other side of the repeater. When the line is cleared the repeater will auto-
matically reconnect the disconnected side.
7.5 Selection of RS-422/485 setting
When an RS-422/485 system is installed it should always form a bus structure. Using
the RD-48, it is possible to produce a star network of several busses. It is important to
terminate RS-422/485 equipment correctly. In standard networks the fail-safe function
should also be connected which is provided to push the unit to a defined state when
the RS-422/485 line becomes undefined. The RD-48 relies on this for operation.
We recommend connection of termination and fal-safe as shown in the application note.