This Design Idea is for low-end, eight-pin, flash-memory, 8-bit microcontrollers, such as the MC68HC908QT4A from Freescale, but it would apply to any 8-bit microcontrollers that use the ADC feature.
This paper describes the design and implementation of a version of the 8051 microcontroller, one of the most commercially used microcontrollers in FPGA with reconfigurable instruction set.