Why does the FX829 generate interrupts for received data when there is no data present?
A. The FSK receiver of the FX829 has a very high sensitivity and in the absence of valid signals will decode noise as data. This is not a fault and is due to the wideband properties of noise where sufficient energy may be present within the FSK decoder’s bandwidth. To prevent erroneous reception the CARRIER DETECT output is used to determine the validity of the received signal. This does not internally gate the FSK receiver so that the designer can implement reception during fades etc. The CARRIER DETECT should be monitored during reception and used to ‘intelligently’ decide whether the data is likely to be valid, suspect or invalid. During periods when there is no data reception the CARRIER DETECT will be predominantly low and the receiver should be turned off. If it is not practical to turn off the receiver then the interrupts can be minimised by masking RXDATAM flag.
