User's Manual

455U Radio Modem Module User Manual
Page 34 © November 2004
4.4.3 Other Parameters
Radio Data Rate
Select the radio data rate which you want to use. Note that modules will only communicate
with each other if they have the same radio data rate. If you select a rate which is faster than
the serial rate, the 455U will automatically set transmission delay parameters in registers S18
and S19 (refer section 3.8). To disable this, deselect the “PLC Mode” box in the Serial
configuration window.
Note that modules will only communicate with each other if they have the same radio data
rate.
CRC Error Checking for transmitted messages
It is normal for error checking to be disabled for unacknowledged mode and enabled for
controlled. However you can select either for either mode, and separately select for the RS-
232 port and the RS485 port. The modem is always able to receive messages both with and
without error checking, so different modems in the system may be configured with different
error checking options. (AT&E).
Data Encryption
Data Encryption may be set to “Disabled”, “Enabled on TX”, or “Forced on RX”. “Disabled”
setting allows the modem to receive both encrypted and unencrypted messages, but the
modem will only transmit unencrypted messages. “Enabled on TX” causes the modem to
transmit encrypted messages and to receive both encrypted and unencrypted messages.
“Forced on RX” causes the modem to transmit encrypted messages and only accept messages
which are encrypted. Note that the encryption keys must be set up in each modem to the same
values to allow the modem to decrypt encrypted data correctly. If incorrect encryption keys
are entered, the data will be forwarded out the correct port, but will be garbled.
Packet Size (bytes)
This selects the maximum number of bytes which will be transmitted in one message. If
more than this number of bytes is input into the 455U, then the module will transmit more
than one message.
The default value is 1024 bytes which is the largest packet value. If you are operating in a
noisy radio environment, then the system may be more reliable if you reduce the maximum
packet size and transmit a larger number of small messages rather than a lesser number of
large messages.
Transmit and Receive Hold-off delay times
A “transmit delay” time and a “receive delay” time can be configured. These parameters may be
used to fine tune and give priority to different 455U units in a system.
• After each message is transmitted, a 455U unit will not transmit another message during the
transmit delay time. This could be used to allow a reply message to be received before the
next message is sent.
• After a message is received, a message will not be transmitted during the receive delay time.
This could be used to delay a reply message until other messages have been sent.