Chapter One
Introduction
Man_455U-D Rev 3.07
Page
11
UNACKNOWLEDGED MODE
ADDRESSED TO ALL UNITS USING
WILDCARD ADDRESS 0
DATA
DATA
DATA
DATA
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
master unit will only link to one
slave at any one time.
Note that Acknowledged mode only applies to the RS-232 port. The RS-485 port always
operates in Unacknowledged mode.
ACKNOWLEDGED MODE
DATA
DATA
NO
DATA
DATA MESSAGE
ACK
