The MX909A is a low power CMOS device containing all of the baseband signal processing and Medium Access Control (MAC) protocol functions required for a high performance GMSK Wireless Packet Data Modem. The MX909A interfaces with a host C and radio modulation/demodulation circuits to deliver reliable two-way transfer of application data over a wireless link. The MX909A assembles application data received from the host C, adds forward error correction (FEC), and error detection (CRC) codes, time-spreads this data by interleaving (burst-error protection) and scrambles (randomizes) the bit pattern. After automatically adding bit and frame sync codewords, the data packet is converted into analog GMSK signals for modulating into the radio transmitter. In the receive mode, the MX909A performs the reverse function using the analog signals from the receivers discriminator. After error correction and removal of the packet overhead, the recovered application data is supplied to the host C. Any CRC detected residual uncorrected errors in the data will be flagged. Readout of the SNR value during receipt of a packet is also provided. The MX909A uses data block sizes and FEC/CRC algorithms compatible with the Mobitex W ide Area Network over-air standard. The format used is suitable for other private applications where the high-speed transfer of data over narrow-band wireless links is required. The MX909A is programmable to operate at standard bit-rates from a wide choice of XTAL/CLOCK frequencies. The MX909A may be used with a 3.0V to 5.5V power supply and is available in the following packages: 24-pin SSOP (MX909ADS), 24-pin SOIC (MX909ADW), 24-pin PLCC (MX909ALH), and 24-pin PDIP (MX909AP).