805U Radio Modem Module
User Manual
Page
34
©
November 2004
the master will transmit the check message up to five times. If there is still no ACK, then the
master will reset the link (DCD reset).
If you enter an “Inactivity Timeout” value, then the 805U will automatically reset the link if
there has been no data transmissions within this time. If you use the link check feature, you
should enter an “Inactivity Timeout” value to reset the link at the slave unit.
It is a good idea to use these timers as it provides a higher level of security for the controlled
mode system (except for “fast operation” systems). Normally a link check time will be
entered at the master unit (for example, 10 seconds), and a inactivity timeout will be entered
at the slave unit (for example, 15 seconds). It is important that the inactivity timeout is
greater than the link check time.
A value of zero disables these parameters.
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 805U 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
It is normal for error checking to be disabled for
transparent mode and enabled for controlled. However
you can select either for either mode. Refer to section 3
of this manual for a description on the operation of error-
checking.
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 805U, then the module will transmit more
than one message.
The default value is 530 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 805U units in a system.
