68k

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The Motorola 680x0/0x0/m68k/68k/68K family of CISC microprocessor CPU chips were 32-bit from the start, and were the primary competition for the Intel x86 family of chips.

Contents 1 Family members 2 Main uses 3 Architecture 4 68050 and 68070 5 Last generation 6 Other variants 7 Desktop competitors 8 Trivia

[edit] Family members

• Generation one (internally 16/32-bit, and produced with 8-, 16-, and 32-bit interfaces)
  • Motorola 68000
  • Motorola 68EC000
  • Motorola 68HC000
  • Motorola 68008
  • Motorola 68010
  • Motorola 68012
• Generation two (fully 32-bit)
  • Motorola 68020
  • Motorola 68EC020
  • Motorola 68030
  • Motorola 68EC030
• Generation three (pipelined)
  • Motorola 68040
  • Motorola 68EC040
  • Motorola 68LC040
• Generation four (superscalar)
  • Motorola 68060
• Others
  • Freescale 683XX (CPU32 aka 68330, 68360 aka QUICC)
  • Freescale ColdFire
  • Freescale DragonBall

[edit] Main uses

The 68k line of processors has been used in a variety of systems, from the modern Texas Instruments TI-89 calculators to the not so modern palm pilot series, and even up to critical control systems of the Space Shuttle. However, they became most well-known as the processors powering desktop computers such as the Apple Macintosh, the Commodore Amiga, the Atari ST, and others. 68k was also the processor of choice in the 1980s for Unix workstations and servers from companies such as Sun Microsystems and SGI.

Today, these systems are either end-of-line (in the case of the Atari), or are using different processors (as is the case for Amiga, Macintosh, Sun and SGI). Since these platforms are now more than a decade old, their original manufacturers are unlikely to support an operating system for this hardware or are even out of business. However, the Linux, NetBSD and OpenBSD operating systems still include support for 68k processors.

The 68k processors were also used in the Sega Mega Drive/Sega Genesis, SNK Neo Geo and Atari Jaguar consoles as the main CPU. Other consoles such as the Sega Saturn also used the 68k as an audio processor and other IO tasks.

Microcontrollers derived from the 68k family have been used in a huge variety of applications. For example, CPU32 and ColdFire microcontrollers have been manufactured in the millions as automotive engine controllers.

[edit] Architecture

People who are familiar with the PDP-11 or VAX usually feel comfortable with the 68000. With the exception of the split of general purpose registers into specialized data and address registers, the 68000 architecture is in many ways a 32-bit PDP-11.

The 68k instruction set can be divided in the following broad categories:

• Load and store (Move.B, Move.W, Move.L)
• Arithmetic (Add, Sub, Mul, Div)
• Bit shifting (left or right, logical or arithmetical)
• Bit rotation (ROR, ROL, ROXL, ROXR)
• Logic operations (And, Or, Not, EOr)
• Type conversion (byte to word and vice versa)
• Conditional and unconditional branches (Bra, BCS, BEq, BNE, BHI, BLO, BMI, BPL, etc.)
• Subroutine invocation and return (BSR, RTS)
• Stack management (push, pop)
• Causing and responding to interrupts
• Exception handling

[edit] 68050 and 68070

Note that there is no 68050; this is because the design that was destined to be the 68050 was eventually released as a version of the 68040. There is also no revision of the 68060, as Motorola was in the process of shifting away from the 68k and 88k processor lines into its new PowerPC business, so the 68070 was never developed. Had it been, it would have been a revised 68060.

Motorola mainly used even numbers for major revisions to the CPU core such as 68000, 68020, 68040 and 68060. The 68010 vas a revised version of the 68000 with minor modifications to the core, and likewise the 68030 was a revised 68020 with some more powerful features, none of them significant enough to classify as a major upgrade to the core.

There was a CPU with the 68070 designation, which was a microcontroller version of the 16/32-bit 68000. This 68070 was used as the main CPU in the Philips CD-i. This CPU was, however, produced by Philips and not officially part of Motorola's 680x0 lineup.

[edit] Last generation

The 4th generation 68060 shared most of the features of the Intel P5 architecture of x86. Had Motorola decided to continue the 680x0 series, the next processor (68080) would likely have resembled Intel's P6 architecture.

[edit] Other variants

After the mainline 68k processors' demise, the 68k family has been used to some extent in microcontroller/embedded microprocessor versions. These chips include the ones listed under "other" above, i.e. the CPU32 (aka 68330), the ColdFire, the QUICC and the DragonBall.

[edit] Desktop competitors

The main competitors in the microcomputer market for generation one were the x86 architecture 8086/8088 first-generation and 80286 second-generation IA-16 chips. For generation two, it was the 80386 IA-32 chips, and for generation three it was the 80486 IA-32 chips. Generation four competed against the Pentium IA-32 chips, but to a lesser extent, as much of the hitherto 68k marketplace was changing to the PowerPC, meaning the death of the 680x0 on the desktop.

[edit] Trivia

• Many people believe that 68K is a play on x86 (i.e. swapped numbers) but both archectures existed when they were both in infancy.

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.