Control issues: How FPGAs can address MCUs' general-purpose I/O scaling wall

But controllers do run into limits. The general-purpose input and output (GPIO) ports available for a microcontroller are usually limited in number. Many applications require more ports than are available on the microcontroller. And because GPIOs are used for a number of functions like serving as a gateway to numerous peripherals and buses, managing LEDs and interrupt sources, oftentimes more is better.

FPGAs, however, can be deployed to overcome this barrier by adding four 8-bit ports to any 8-bit microcontroller. With the broad IP libraries available from FPGA vendors today, it's a relatively straightforward endeavor. Take the 8051s soft microcontroller core. It can be configured as an 8-bit microcontroller, without sacrificing power budget, cost or board real estate.

The 8051s: History, Compatibility
Core8051s is an ASM51-compatible microcontroller core that can run programs written for the 8051. It contains the main 8051 core logic but no peripheral logic. Core8051s has an APB bus interface that can be used like the SFR bus to easily expand the functionality of the core by connecting it to existing APB IP peripherals. This allows users to configure the core with the peripheral functions, such as I/O ports that they need for their application.

It also features a high-performance 8-bit microcontroller, one clock per instruction and can be used with existing 8051 tools and code, among other things.