User's Manual

905U-D Radio Modem Module User Manual
Page 24 © May 2000
It is possible to configure different units in the same system with different operating modes,
however the system will not operate. A 905U-D unit configured in one mode will not process
a message received from a unit in the alternate mode.
Error Check ?
Error-checking may be configured in both transparent and controlled mode. When the error-
check is configured, two additional bytes are attached to the end of each message. These
bytes are used to detect any corruption of the data when it is received at another 905U-D unit.
When a unit with error-check configured receives a radio message, it will not output data
until it has received the whole message and ensures that the error-check is correct. If the
unit does not have error-check configured, then it will output data as it is received. Hence
operation of the units is faster if error-check is not configured.
We recommend that units in the same system have the same error-check configuration,
however it is possible for users to configure the units differently. If a unit without error-check
configured receives a message which includes an error-check, then the unit will treat the
additional two bytes as data and output them to the host device. If a unit with error-check
configured, receives a message without an error-check, it will treat the last two data bytes
as the error check - the error-check will always be incorrect and no data will be output.
Error-check is strongly recommended for controlled mode operation. If error-check is not
configured, then a 905U-D unit will transmit an acknowledgment message (ACK) whenever
it receives a radio message, without checking for errors. If error-check is configured, the
unit will only transmit an ACK message if the error-check is correct. If it is incorrect, an error
message (NACK) is returned to the source address.
Autoconnect or Host-connect modes?
If the 905U-D is connected to a PC and the PC will automatically set-up the 905U-D on start-
up, then a host-connect mode should be used (modes 0 – 3). In host-connect, the 905U-D
will start up in configuration mode.
If you want the 905U-D to start up in operating mode, then use the autoconnect modes (4 –
7).
3.6 Operating Problems
Most operating problems relate to an inadequate radio path, or radio interference. Before
installing a system, bench test the complete system with the 905U-D units near each other.
This test eliminates the radio path or interference as a factor, and ensures that the system
will operate in the way that you want.
If the bench test does not give adequate performance, then you need to adjust the
configuration parameters. We recommend that you do not install the system until you are
happy with the bench test performance.
If a system gives poor performance after it is installed, check the adequacy of the radio path
- refer to the Diagnostics Section 6.
Interference will only cause a problem if the amplitude of the interference is comparable to
the radio signal from the 905U-D units. If the interference level is relatively small, then it will
not affect the performance of the system. If interference is causing a problem, try to improve