Motorola's 6809 was a source-code compatible enhancement of the earlier 6800, but which had some 16-bit functions including in its maths handling.

However, although its 16-bit features made it one of the most powerful 8-bit processors around, it was significantly more expensive than the competition, especially MOS Technology's 6502 and Zilog's Z80. 

It was also released at a time when true 16-bit processors like Intel's 8086 were appearing, which it couldn't compete with as it was still an 8-bit chip.

As such, it was never hugely popular, although it was used in Dragon Data's micros as well as the Tandy Colour Computer, making the two loosely compatible. It also led to one of the first multi-user operating systems aimed at "home" computers - Microware's OS-9.