Chapter 18. 68000-Series Computers

All is flux, nothing stays still.

Heraclitus, Diogenes Laertius’ Lives of Eminent Philosophers

In this chapter, we’ll take a look at a 32-bit processor that has been around for quite some time and has evolved into a plethora of controllers and embedded processors. The 68000 (also known as the “68k”) is produced by Freescale Semiconductor and is licensed by several other manufacturers. The range of 68000-based processors is large (check out the manufacturers’ web sites for a list of processors and their features). The number of applications that the 68000 has found its way into is enormous. You can even get 68000s as soft cores for FPGAs, which means you place a 68000 CPU in the midst of your programmable logic, all on the one chip.

The Motorola[*] MC68000 was introduced in 1979 as the successor to its 8-bit 6800 family. It featured a large address space, 32-bit registers, a large number of addressing modes, and an enlarged instruction set with over 1,000 opcodes. It was designed with the intention of running multitasking operating systems, specifically Unix. Its use in Unix machines has now long since passed, having been usurped by more advanced RISC processors. The 68000 processor was also used in the original Macintosh computers, as well as in the Atari ST, the Commodore Amiga, and Jef Raskin’s CAT computer, all long extinct.


For an interesting overview of the CAT, read Jef Raskin’s The Humane Interface (Addison-Wesley Professional). He discusses ...

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