FX909A

The FX909A is a CMOS integrated circuit that contains all of the baseband signal processing and Medium Access Control (MAC) protocol functions required for a high performance GMSK Wireless Packet Data Modem. FX909A interfaces with the modem host processor and the radio modulation/demodulation circuits to deliver reliable two-way transfer of the application data over the wireless link.

The FX909A assembles application data received from the processor, adds error correction code (FEC), adds error detection code (CRC), time-spreads this data by interleaving (burst-error protection) and scrambles (randomises) the bit pattern. After adding bit and frame sync codewords,it converts the packet into analogue GMSK signals for modulating the radio transmitter.

In receive mode, the FX909A performs the reverse function using the analogue signals from the receiver discriminator. After error correction and removal of the packet overhead, the recovered application data is supplied to the processor. Any residual uncorrected errors in the data will be flagged. A readout of the SNR value during receipt of a packet is also provided.

The FX909A uses data block sizes and FEC/CRC algorithms compatible with the Mobitex Wide Area Network over-air standard. The format used is suitable for other private applications which require the high-speed transfer of data over narrow-band wireless links. The FX909A is programmable to operate at most standard bit-rates from a wide choice of Xtal/clock frequencies.