The development of an 8 kbps GMSK-like modem for Mobitex

The 1200/8000 b/s GMSK-like modem utilizing a digital signal processor (DSP) and the required support circuitry is being developed. The modem functions are implemented using a DSP-based assembler. Both data transmission speeds are accommodated and are user selectable depending upon the position of a hardware selection switch (prototype only). The design eliminates the need for external DSP memory, as both the transmit and receive software, each restricted in size to 512 words of 24 bits, will reside on the DSP while being used. The DSP forms the heart of the modem. The controller section makes use of an Intel microprocessor, RAM, PROM, EEPROM, a gate array to provide an interface to the radio, and a combination of a communications controller with EIA drivers to create a standard user terminal interface.<>