The P89C669 represents the first Flash microcontroller based on Philips Semiconductors' new 51MX core. The P89C669 features 96 kbytes of Flash program memory and 2 kbytes of data SRAM. In addition, this device is equipped with a Programmable Counter Array (PCA), a watchdog timer that can be configured to different time ranges through SFR bits, as well as two enhanced UARTs and byte based I2C-bus serial interface. Philips Semiconductors' 51MX (Memory eXtension) core is an accelerated 80C51 architecture that executes instructions at twice the rate of standard 80C51 devices. The linear address range of the 51MX has been expanded to support up to 8 Mbytes of program memory and 8 Mbytes of data memory. It retains full program code compatibility to enable design engineers to re-use 80C51 development tools, eliminating the need to move to a new, unfamiliar architecture. The 51MX core also retains 80C51 bus compatibility to allow for the continued use of 80C51-interfaced peripherals and Application Specific Integrated Circuits (ASICs). The P89C669 provides greater functionality, increased performance and overall lower system cost. By offering an embedded memory solution combined with the enhancements to manage the memory extension, the P89C669 eliminates the need for software work-arounds. The increased program memory enables design engineers to develop more complex programs in a high-level language like C, for example, without struggling to contain the program within the traditional 64 kbytes of program memory. These enhancements also greatly improve C Language efficiency for code size below 64 kbytes. The P89C669 device contains a non-volatile Flash program memory that is both parallel programmable and serial In-System and In-Application Programmable. In-System Programming (ISP) allows the user to download new code while the microcontroller sits in the application. In-Application Programming (IAP) means that the microcontroller fetches new program code and reprograms itself while in the system. This allows for remote programming over a modem link. A default serial loader (boot loader) program in ROM allows serial In-System programming of the Flash memory via the UART without the need for a loader in the Flash code. For In-Application Programming, the user program erases and reprograms the Flash memory by use of standard routines contained in ROM. The 51MX core is described in more detail in the 51MX Architecture Reference.