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| }}</ref> The 68008 was available with 20 or 22 address lines (respective to 48-pin or 52-pin package) which allowed 1 MB or 4 MB address space versus the 16 MB addressable on the 68000. The 68008 was designed to work with lower cost and simpler 8-bit memory systems. | }}</ref> The 68008 was available with 20 or 22 address lines (respective to 48-pin or 52-pin package) which allowed 1 MB or 4 MB address space versus the 16 MB addressable on the 68000. The 68008 was designed to work with lower cost and simpler 8-bit memory systems. Because of its smaller data bus, it was roughly half as fast as a 68000 of the same clock speed.<ref name=68kusermanual /> It was still faster than competing 8-bit microprocessors,{{dubious|date=September 2021|reason=Performance claims come from vendor}} because internally the 68008 behaves identically to the 68000 and has the same ].{{sfn|Motorola|1993|page=1-2}} | ||
| Because of its smaller data bus, it was thought to be roughly half as fast as a 68000 of the same clock speed.<ref name=68kusermanual /> But the difference in performance between them is much less marked than expected, because both CPUs have a instruction pipeline, which allows the processor to get on with fetching the data "piecemeal" while the instruction is being decoded. So, by the time the data is needed, it's usually in the pipeline and the 68008 doesn't have to wait for it to be fetched, eight bits at a time. <ref>http://www.users.globalnet.co.uk/~jg27paw4/yr05/yr05_43.htm</ref> Even without the pipeline, it was still faster than competing 8-bit microprocessors,{{dubious|date=September 2021|reason=Performance claims come from vendor}} because internally the 68008 behaves identically to the 68000 and has the same ].{{sfn|Motorola|1993|page=1-2}}. In the "Byte" magazine of September of 1986, in page 206, a diagram comparing all 68K cpus up to then, shows that the 68008 could actually perform with almost 80% of the performance of the 68000, at the same MHz<ref>https://archive.org/details/byte-magazine-1986-09/page/n217/mode/2up</ref>. | |||
| Motorola ended production of the 68008 in 1996.<ref>, 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.</ref> | Motorola ended production of the 68008 in 1996.<ref>, 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.</ref> | ||
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The Motorola 68008 is an 8/32-bit microprocessor introduced by Motorola in 1982. It is a version of 1979's Motorola 68000 with an 8-bit external data bus, as well as a smaller address bus. The 68008 was available with 20 or 22 address lines (respective to 48-pin or 52-pin package) which allowed 1 MB or 4 MB address space versus the 16 MB addressable on the 68000. The 68008 was designed to work with lower cost and simpler 8-bit memory systems. Because of its smaller data bus, it was roughly half as fast as a 68000 of the same clock speed. It was still faster than competing 8-bit microprocessors, because internally the 68008 behaves identically to the 68000 and has the same microarchitecture.
Motorola ended production of the 68008 in 1996.
Details
The 68008 is an HMOS chip with about 70,000 transistors; with a speed grade of 8 and 10 MHz. There are two versions of the chip. The original is in a 48-pin dual in-line package with a 20-bit address bus, allowing it to use up to 1 megabyte of memory. A later version is in a 52-pin plastic leaded chip carrier; this version has a 22-bit address bus and can support 4 megabytes of RAM.
Usages
The Sinclair QL microcomputer and Luxor ABC 1600 use the 68008 as their main processor.
References
- ^ Motorola (1993). "M68000 8-/16-/32-Bit Microprocessors User's Manual, Ninth Edition" (PDF). NXP Semiconductors.
- Motorola 1993, p. 1-2.
- 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.
- Motorola 1993, p. 3-4.
External links
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