One of the struggles with vintage computer systems is that many of the ICs in them have no modern-day version that you can just purchase and drop-in. Creating replacements that use modern-day ICs inside has consequently become a popular direction, with [Philip Smart]’s TranZPUter being one such example.
Standing for ‘transformable ZPU Computer’, the tranZPUter is transformable in the sense that it features an FPGA or MCU and the initial iteration targeting the ZPU Evo CPU design. This has led to a number of variants of this concept, including a version targeting the Z80, the 6502 and 6809. These are based around the RP2350B MCU, using its PIO peripheral to great effect.
Of these the Motorola 6809 is probably the lesser known MPU, having been launched in 1978 as an 8-bit MPU with some 16-bit features that could beat the 6502 in many metrics courtesy of its more advanced hardware. It being more expensive led to it only being used in systems like the TRS-80 Color, Dragon 32/64, SuperPET and a whole range of arcade systems.
If you have any of those 6809-based systems and the MPU gave up the ghost, you can drop in the Pico6809 board featuring said RP2350B MCU as well as an ESP32 co-processor. Currently it targets the Dragon 32/64 systems, adding not just a fresh MPU, but also adds virtual floppy and cassette devices as well as network support as options.
Overall it seems like a pretty extensive project that might already have found purchase within the retrocomputing community.