since 1977 (earliest usage recorded on this site was 1976)
The Motorola 6809 is an 8-bit (with some 16-bit features) microprocessor CPU from Motorola, introduced circa 1977-78. It was a major advance over both its predecessor, the Motorola 6800, and the related MOS Technology 6502.
Among the significant enhancements introduced in the 6809 were the use of two 8-bit accumulators (A and B, which could be combined into a single 16-bit register, D), two 16-bit index registers (X, Y) and two 16-bit stack pointers. The index and stack registers allowed very advanced addressing modes. Program counter relative addressing allowed for the easy creation of position-independent code, while a user stack pointer (U) facilitated the creation of reentrant code.