2090 for Mac

From Stephan Kleinert:

The Busch microtronic 2090 was a 4-bit computer system, similar to the KIM-1, but targeted at the educational market. It was sold mainly in Germany.
It had the following features:
- TMS-1600 microprocessor with custom monitor program on chip - 500kHz clock - 6-digit 7-segment LED display - hexadecimal keypad with extra functions - 4-bit TTL in- and output - 6 LEDs show the state of the outputs and of carry and zero flags. - 1Hz clock generator - 512 Bytes (or 1024 "Nibbles") of RAM - 256 instruction program memory - 32 4-bit registers, 16 of which were accessible without bankswitching - support for optional tape interface - 7 programs in firmware
Features of this program:
- emulates the full 2090 instruction set - can load and save 2090 programs - 2 extra buttons can be wired to the 2090's 4-bit-inputs - the clock output can be wired to the 2090's 4-bit-inputs - one of the outputs can be wired to the system beeper