Chapter Three
Operation
Man_805U Rev 1.8
Page
27
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 805U 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.
3.8
Serial / Radio Rates
The 805U will operate most efficiently when the serial and radio data are configured to the
same value. If the serial data rate is less than the radio rate, there is a risk that the radio will
empty the input buffer to quickly, resulting in a single input message being broken into more
than one output messages. Many host protocols such as those used by PLC’s, will not accept
a message being broken.
To avoid this occurring, the 805U will automatically delay the radio transmission starting.
This is called “PLC Mode”. The radio will not start transmitting until a certain number of
bytes have been input into the input buffer. The 805U calculates the number of starting bytes
depending on the values of the configured serial and radio rates. The number of bytes to start
transmitting is stored in register S18 (refer section 4 “Configuration”) - when a
configuration is entered whereby the serial rate is less than the radio rate, the 805U will
automatically enter an appropriate value in S18. The user can change this value. If the serial
rate is the same as the radio rate, or more, than there is no delay.
There is an automatic protection - if a certain time has elapsed and the number of starting
bytes has not been input, then the radio will start transmitting. This is an override protection.
The 805U will automatically calculate the override time based on the configured serial rate
and S18 (the number of bytes required to start). The override time is stored in register S19 -
this value can also be changed by the user.
3.9
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 805U 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. It is not necessary to connect antennas, however a small
length of wire should be inserted into the middle pin of the coaxial connector - this will act
as an antenna.
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 805U 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
