A Harward architecture Turing-complete ;) machine with 16 bit circular buffer for data (the "data tape"), a circular buffer for 16 2-bit code words ("code tape"), a 1-bit accumulator, and a 1-bit "ALU" with 2 single-operand commands: CPY and INV (codes 00 and 01), and 2 double-operand commands using the acc: OR and NAND (codes 10 and 11). You can figure out how to program it yourself :D (hint: use push buttons and start/stop the 555 clock, slower simulation speed can help...)
