Retrocomputing Stack Exchange
Retrocomputing Stack Exchange

Questions tagged [m68k]

For questions about processors in the Motorola 68k (68000 series) range. Commonly used in Amiga, Atari ST, Macintosh, Sinclair QL and Sharp X68000 computers.

Use this tag for questions that apply to processors in the m68k (otherwise known as 68xxx) range from Motorola.

For questions regarding a specific processor use an individual tag, e.g.

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How does the 68060 branch predictor work?

The 68060 had a branch predictor that improved the cycle count of branches that tended to go one way or the other. Apparently it did not handle branches that alternated or had some kind of pattern to when they were taken. How did this branch…
Omar and Lorraine
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What do the "byte-select signals" in the 68000 do?

Got a question about how the 68000 addresses memory. Wikipedia says: The 68000 has a 24-bit external address bus and two byte-select signals "replaced" A0. Here is an image of the chip's pins: As Wikipedia says, A0 is not there. So instead,…
Omar and Lorraine
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68020 addressing mode suitable for page printing?

Wikipedia's article for MC68020 sports this paragraph: Addressing modes The new addressing modes added scaled indexing and another level of indirection to many of the pre-existing modes, and added quite a bit of flexibility to various indexing…
user180940
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How did multiply instructions work in the various 68ks?

pndc says about the 68000: the [...] MULU/MULS instructions are very slow, taking about 70 cycles. The exact number of cycles is data-dependent because the microcode uses an iterative algorithm.) So, (assuming that pndc is correct and the…
Omar and Lorraine
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