The GP4020 is a complete digital baseband processor for a Global Positioning System (GPS) receiver. It combines the 12-channel correlator function of the GP2021 with an advanced ARM7TDMI (Thumb) microprocessor to achieve a higher level of integration, reduced system cost, reduced power consumption and added functionality. The GP4020 complements the GP2015 and GP2010 C/A code RF downconverters available from Zarlink Semiconductor. The correlator section contains 12 identical tracking module blocks, one for each channel. Each channel contains all the components necessary for acquiring and tracking the received signal, and also contains other functional blocks, which are used to produce part of the measurement data set. Individual channels may be deactivated for systems not requiring full 12-channel operation and thus allowing for reduced power consumption and processor loading. The microprocessor section contains the Firefly MF1 microcontroller core, which includes an ARM7TDMI with a Thumb instruction de-compressor plus the Firefly BILD module. Also included are a second UART, BILD Serial I/O, General I/O and Watchdog functions.