IKCH-44 6809 Emulator
The IKCH-44 6809 emulator board consists of a Raspberry Pi PICO that pretends it's a 6809 running with a 6 MHz clock. Generally, the state machine sits in an idle read of $FFFF, and occasionally does a real read or write cycle. Cycles are done by squirting an address (and optional data) to 16 (or 24) bits worth of 74HC595 and modifying one cycle of the PIO-based state machine. The PIO state machine is responsible for latching read data (if doing a real read cycle) into the parallel side of the shift register. The foreground PICO program then grabs the data from the shift register. For a write, the PICO foreground sets up the data in the '595 latches and diverts the state machine to perform one write cycle.