User's Manual

455U-D Radio Modem Module User Manual
Page 10 © Jan 2008
• to all modems in the system, as a broadcast message by using the wildcard address 0. The
wildcard address is
used to send a message
to a group of modems.
Data received at the serial
port is transmitted out of
the radio port, addressed to
the configured destination
455U-D module, or to all
modules by using address
0. Data received from the
radio with the correct
addressing is transmitted
out of one of the serial
ports (RS232 or RS485).
Prior to transmitting, units will listen to the radio channel to ensure that it is clear - units will
hold off from transmitting until the radio channel is clear.
At the RS232 port, the CTS pin can be configured to go high while there is space in the input
data buffer - otherwise it is always high.
Host devices should provide a suitable protocol to ensure that error checking, handshaking and
implementation of an appropriate re-transmission scheme is provided. This mode of operation
is particularly suited to devices designed to operate over a multidrop network, such as PLC
systems designed for operation over a RS-485 network.
If error checking is not configured at the receiving unit, data will start to be output
immediately after the first byte of data has been received. If error checking is configured, data
will be output approx 1mSec after the end of the message. For example, a message with 20
bytes of data transmitted at 19200 bits/sec will begin to be output approx 23 msec after the
data is input, if there is no error checking, or 31 msec after the data is input if error checking is
configured - this assumes the minimum lead-in time of 20 msec is configured.
1.3 Acknowledged Mode
In Acknowledged mode,
data is transferred between
the RS-232 ports of two
modules (that is, a point to
point link). One of the
modules is configured as a
“master” (or initiator) unit
and the other as a “slave”
(or responder) unit. There
can be many slave units in
the system, however the
UNACKNOWLEDGED MODE
ADDRESSED TO ALL UNITS USING
WILDCARD ADDRESS 0
DATA
DATA
DATA
DATA
ACKNOWLEDGED MODE
DATA
DATA
NO
DATA
DATA MESSAGE
ACK