Motorola 68008
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The Motorola 68008 is an 8/16/32-bit microprocessor made by Motorola. It is a version of the Motorola 68000 with an 8-bit external data bus, as well as a smaller address bus.
The original 68000 had a 24-bit address bus and a 16-bit data bus. These relatively large buses made it hard to design a low-cost system around the 68000; they were difficult to lay out on a circuit board and needed a lot of supporting circuitry. A 16-bit data bus also required twice as many memory chips as an 8-bit one.
The 68008, introduced in 1982, was designed to work with low-cost 8-bit memory systems. Because of its smaller data bus, it was only about half as fast as a 68000 of the same clock speed. However, it was still faster than competing 8-bit microprocessors, because the 68008's internal architecture was more powerful and efficient.
Except for its smaller data and address buses, the 68008 behaved identically to the 68000 and had the same internal organization and microarchitecture.
The 68008 was an HMOS chip with about 70000 transistors; it came in 8 and 10 MHz speed grades. There were two distinct versions of the chip. The original version came in a 48-pin dual in-line package and had a 20-bit address bus, allowing it to use up to 1 mebibyte of memory. A later version came in a 52-pin plastic leaded chip carrier; this version provided a 22-bit address bus and could support 4 mebibytes of memory.
Very few computer systems used the 68008 as the main processor; the Sinclair QL personal computer is the best known of these. However, the 68008 was popular in embedded systems.
Motorola ended production of the 68008 in 1996.[1]
[edit] Notes
- ^ comp.sys.m68k Usenet posting, May 16, 1995; also see other posts in thread. The end-of-life announcement was in late 1994; according to standard Motorola end-of-life practice, final orders would have been in 1995, with final shipments in 1996.
[edit] References
M68000 8-/16-/32-Bit Microprocessors User's Manual, Ninth Edition
[edit] External links
- A small 68008 design can be found here.
| List of Motorola/Freescale microprocessors | |
|---|---|
| The 6800 family : | 6809 (see also: Hitachi 6309) |
| 68000 family : | 68000 | 68008 | 68010 | 68012 | 68020 | 68030 | 68040 | 68060 | ColdFire | DragonBall |
| Low-cost variants: | 68EC000 | 68EC020 | 68EC030 | 68EC040 | 68LC040 |
| Pre-PowerPC RISC : | 88000 |
| Floating-point coprocessors : | 68881, 68882 |
| PowerPC family : | PPC 75x ("PowerPC G3") | PPC 74xx ("PowerPC G4") | PowerQUICC |
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