System level design objectives of cost, performance and time-to- market require a hardware/software co-design methodology comprising realization of custom hardware along with software execution on an embedded processor. In this context is described the architecture of AIM250, a high end mixed signal microcontroller for instrumentation, measurement and control systems. The embedded processor has a concurrently executing DSP engine and a 12-bit analog interface to external world making it one of the more advanced among contemporary microcontrollers. The special emphasis on design reconfigurability made it possible for it to achieve FPGA type flexibility in peripheral modules with negligible silicon overhead.