Motorola 68012
The Motorola MC68012 processor is a 16/32-bit microprocessor from the early 1980s. It is an 84-pin PGA[1] version of the Motorola MC68010. The memory space was extended to 2 GB, and a read-modify-write cycle (RMC) pin, indicating that an indivisible read-modify-write cycle in progress, was added, in order to help the design of multiprocessor systems with virtual memory.[2][3] All other processors had to hold off memory accesses until the cycle was complete. All other features of the MC68010 were preserved.
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The expansion of the memory space caused an issue for any programs that used the high byte of an address to store data, a programming trick that was successful with those processors that only have a 24-bit address bus (68000 and 68010). A similar problem affected the 68020.
Notes and references
- "Motorola 68012 (MC68012) microprocessor family".
- MC68010/MC68012 16-/32-Bit Virtual Memory Microprocessors (PDF). Motorola Semiconductor. May 1985.
- Avtar, Singh; Triebel, Walter A. (1991). 16-Bit and 32-Bit Microprocessors: Architecture, Software, and Interfacing Techniques. Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 978-0138121570.