Description
The FX/MX919B 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 4-level FSK Wireless Packet Data Modem. Half-duplex .
The FX/MX919B is backwards compatible with the FX/MX919A but offers better performance during radio link fading and selectable Tx symbol shapes.

The FX/MX919B assembles application data received from the processor, adds forward error correction (FEC) and error detection (CRC) information and interleaves the result for burst-error protection.
After adding symbol and frame synchronisation codewords, it converts the packet into a filtered 4-level analogue baseband signal for modulating the radio transmitter. In receive mode, the FX/MX919B performs the reverse function using the analogue baseband 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 FX/MX919B uses data block sizes and FEC/CRC algorithms suitable for applications which require the high-speed transfer of data over narrow-band wireless links. The device is programmable to operate at most standard bit-rates from a wide choice of Xtal/clock frequencies.