Motorola 68000

As one of the first widely available processors with a 32-bit instruction set, large unsegmented address space, and relatively high speed for the era, the 68k was a popular design through the 1980s.

It was widely used in a new generation of personal computers with graphical user interfaces, including the Macintosh 128K, Amiga, Atari ST, and X68000.

[9] By late 1976, the sales book was flat and the division was only saved by a project for General Motors that turned into a huge product line for engine control and other tasks.

[12] Crook formed the Motorola Advanced Computer System on Silicon (MACSS) project to build the design and hired Tom Gunter to be its principal architect.

They wanted the design to not only win back microcomputer vendors like Apple Computer and Tandy, but also minicomputer companies like NCR and AT&T.

At the time, 64-pin dual inline package (DIP)s were "large, heavy-cost" systems and "just terrible", making that the largest they could consider.

To make it fit, Crook selected a hybrid design, with a 32-bit instruction set architecture (ISA) but 16-bit components implementing it, like the arithmetic logic unit (ALU).

[13][a] By the mid-1970s, Motorola's MOS design techniques had become less advanced than their competition, and their fabrication lines at times struggled with low yields.

[19] This was an investment aimed at catching the competition: even upstart semiconductor companies such as Zilog and MOS Technology had introduced CPUs fabricated on depletion-mode NMOS logic before Motorola did.

In fact, Motorola may have substantially lagged contemporaries in phasing out enhancement mode and metal gate, with Gunter recollecting that the 68000 itself had to succeed despite initially adopting a metal-gate design.

[20] Though the point about playing catch-up is clear, this could not have been an entirely accurate summary because Motorola's 1976 datasheets, predating the inception of the MACCS project, denote the majority of its 6800 family in silicon-gate.

[22] Whatever the degree of Motorola's process and manufacturing deficits in the early days, the team was undeterred and would not compromise in its pursuit of a microprocessor with industry-leading performance.

These included Hitachi (HD68000), who shrank the feature size to 2.7 μm for their 12.5 MHz version,[25] Mostek (MK68000), Rockwell (R68000), Signetics (SCN68000), Thomson/SGS-Thomson (originally EF68000 and later TS68000), and Toshiba (TMP68000).

Both the physical design and test program were transferred to Rochester from NXP to continue to supply an authorized source to the market.

[31] This chip resembles the 68HC000 in most respects, but its data bus can operate in either 16-bit or 8-bit mode, depending on the value of an input pin at reset.

[32] In 1996, Motorola updated the standalone core with fully static circuitry, drawing only 2 μW in low-power mode, calling it the MC68SEC000.

[33] Motorola ceased production of the HMOS MC68000, as well as the MC68008, MC68010, MC68330, and MC68340 in on June 1, 1996,[34][35] but its spin-off company Freescale Semiconductor was still producing the MC68HC000, MC68HC001, MC68EC000, and MC68SEC000, as well as the MC68302 and MC68306 microcontrollers and later versions of the DragonBall family.

By the mid-1980s, falling production cost made the 68000 viable for use in personal computers starting with the Apple Lisa and Macintosh, and followed by the Amiga, Atari ST, and X68000.

Among the systems benefited from having a 68000 or derivative as their microprocessor were families of programmable logic controllers (PLCs) manufactured by Allen-Bradley, Texas Instruments and subsequently, following the acquisition of that division of TI, by Siemens.

The 683XX microcontrollers, based on the 68000 architecture, are used in networking and telecom equipment, television set-top boxes, laboratory and medical instruments, and even handheld calculators.

[46] Certain arcade games (such as Steel Gunner and others based on Namco System 2) use a dual 68000 CPU configuration,[47] and systems with a triple 68000 CPU configuration also exist (such as Galaxy Force and others based on the Sega Y Board),[48] along with a quad 68000 CPU configuration, which has been used by Jaleco (one 68000 for sound has a lower clock rate compared to the other 68000 CPUs)[49] for games such as Big Run and Cisco Heat; another, fifth 68000 (at a different clock rate than the other 68000 CPUs) was used in the Jaleco arcade game Wild Pilot for input/output (I/O) processing.

Motorola's intent with the internal 32-bit address space was forward compatibility, making it feasible to write 68000 software that would take full advantage of later 32-bit implementations of the 68000 instruction set.

For example, early (pre-7.0) versions of Apple's Mac OS used the high byte of memory-block master pointers to hold flags such as locked and purgeable.

Later versions of the OS moved the flags to a nearby location, and Apple began shipping computers which had "32-bit clean" ROMs beginning with the release of the 1989 Mac IIci.

(Note that an exception routine in supervisor mode can also save the user stack pointer A7, which would total 8 address registers.

However, the dual stack pointer (A7 and supervisor-mode A7') design of the 68000 makes this normally unnecessary, except when a task switch is performed in a multitasking system.)

Several companies did succeed in making 68000-based Unix workstations with virtual memory that worked by using two 68000 chips running in parallel on different phased clocks.

For example, the unsigned multiply instruction takes (38+2n) clock cycles to complete where 'n' is equal to the number of bits set in the operand.

The 68EC000 was used as a controller in many audio applications, including Ensoniq musical instruments and sound cards, where it was part of the MIDI synthesizer.

In contrast, the code below is for a stand-alone function, even on the most restrictive version of AMS for the TI-89 series of calculators, being kernel-independent, with no values looked up in tables, files or libraries when executing, no system calls, no exception processing, minimal registers to be used, nor the need to save any.