View source for Category:6800 Assembly

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[[Category:Assembly]]
The 6800 was the central processing unit of a family of integrated circuits and development boards designed by Motorola in the early 1970s, and marketed heavily beginning in 1975.  Like its contemporary, the Intel 8080, it was a microprocessor with an 8-bit data bus and a 16-bit address bus, offered in a 40-pin DIP.

It has been stated that the design team loosely based the assembly language of the 6800 on the DEC PDP-11, although cost concerns necessitated that it be a subset of the much larger and more expensive DEC design.

From a programmer's standpoint, the 6800 possessed two 8-bit accumulators (A and B), two 16-bit pointer registers (X and S), a 16-bit instruction pointer, and an 8-bit flag register (P).  Although the 8080 had more registers and a faster base clock, real-world performance and machine-code density were quite similar, due to the more flexible addressing modes and lower clock-per-instruction ratio of the 6800.  PC-relative branching instructions (with signed 8-bit displacements) and 8-bit (direct-page) addressing options also helped the 6800 in this regard.  The hobbyists of the day had a tendency to fall into two different groups (the 8xxx and 6xxx 'camps'), and countless contests and debates ensued, with each group claiming that their 'family' was superior.  It was quite rare to see a small-computer enthusiast in the late 1970s who didn't have a strong preference for one over the other.

The 6800 spawned many offshoots and offspring, like the MOS Technology 65xx family, the "upward-compatible" Motorola 6809, and numerous micro-controllers.  68xx-based systems were prevalent in the late 1970s and early 1980s, in household, business, and automotive applications.  The 6800's popularity in home computers, however, was easily eclipsed by the 65xx family of microprocessors, largely due to the lower hardware cost and comparable performance of the 65xx family.  The 8080 suffered a similar fate, at the hands of the Zilog Z-80 (due mostly to the Z-80's richer and more versatile instruction set).

The Motorola 68000, designed in the late 1970s, was the popular and much more capable successor to the 6800, and although their assembly languages both share a similarity to the DEC PDP-11 (a model of elegance and orthogonality), they are all mutually incompatible.