Programmable logic devices have claimed their place in the hobbyist world, with more and more projects showing up that feature either a CPLD or their bigger sibling, the FPGA. That place is rightfully earned — creating your own, custom digital circuitry not only adds flexibility, but opens up a whole new world of opportunities. However, this new realm can be overwhelming and scary at the same time. A great way to ease into this is combining the programmable logic with a general purpose MCU system that you already know and are comfortable with. [Just4Fun] did just that with the CPLD Fun Board, a development board connecting an Arduino compatible STM32F103 Cortex-M3 controller to an Altera MAX II CPLD.
The PCB itself has some standard development board equipment routed to the CPLD: LEDs, buttons, a seven-segment display, and additional GPIO. The rest of the CPLD’s pins are going straight to the STM32 and its SPI, I2C and UART pins. Let’s say you want to create your own SPI device. With the CPLD Fun Board, you can utilize all the pre-existing libraries on the STM32 and fully focus on the programmable logic part. Better yet, every connection from MCU to CPLD has its own pin header connection to attach your favorite measurement device for debugging. And in case you’re wondering — yes, you can attach external hardware to those connectors by setting either MCU or CPLD pins to Hi-Z.
The downside of all this is the need for proprietary design software and a dedicated programmer for the CPLD, which sadly is the everyday reality with programmable logic devices. [Just4Fun] did a great job though writing up a detailed step-by-step tutorial about setting up the environment and getting started with the board, but there are also other tutorials on getting started with CPLDs out there, in case you crave more.