Tait TB8100 - Digital Signal Processor (DSP)

30 Reciter Circuit Description TB8100 Service Manual
© Tait Electronics Limited September 2006
2.1.2 Digital Signal Processor (DSP)
The DSP is responsible for software processing of digitised signals in the
receiver and transmitter. The processing word width is 16-bit fixed point.
There are 96 kilobytes of on-chip program memory, and 64 kilobytes of
on-chip data memory. Although no external memory is used, the external
memory interface is connected to the DDC for initialisation and
configuration.
Transmit Functions The DSP performs the following transmit functions:
■ CTCSS and DCS sub-audible signal generation
■ CWID generation
■ pip tone generation
■ audio filtering: including removal of sub-audible components, pre-
emphasis and low pass filtering
■ signal path switching
■ signal level adjustment
■ peak FM deviation limiting
■ FM signal generation by controlling the dual point modulator
■ calibration parameter estimation
■ line level monitoring.
Receive Functions The DSP performs the following receive functions:
■ detection of CTCSS and DCS signalling
■ audio filtering: including removal of sub-audible components, de-
emphasis and low pass filtering
■ signal path switching
■ signal level adjustment
■ FM demodulation of the base band signal
■ RSSI measurement for monitoring and RSSI signal voltage output
■ SINAD measurement
■ measurement and detection for control of the audio mute
■ calibration parameter estimation
■ line level monitoring.
Serial Ports The DSP has three synchronous serial ports. Serial port 1 is connected to
the DDC and receives base band samples. Serial port 2 is connected to the
three CODECs (encoder/decoder). Serial port 3 is not used.