(HD6309) hitachi's version of the motorola 6809 microprocessor. Compatible with the 6809, it added two new eight-bit registers that could be added to form a second 16-bit register, and all four eight-bit registers could form a 32-bit register. It also featured division, and some 32-bit arithmetic and was generally 30% faster in native mode. This information, surprisingly, was never published by Hitachi.

technical reference.