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THE CAPTAIN IS BACK

by Tom Cantrell

Start ı Roots ı ı180s Turn ı eZ Way Out ı Captain at the Crossroads ı Sources

eZ WAY OUT

Most daring of all, Zilog has announced the eZ80, depicted in Figure 2. Although I donıt have enough technical specs in hand to get a complete picture, on paper the eZ80 appears to be quite a radical extension to the Z80 architecture. As mentioned earlier, Zilogıs previous efforts to upgrade the architecture havenıt been especially successful. Are the prospects for the eZ80 any better? Hereıs whatıs known so far.

(Click here for figure)

Figure 2ıAlthough the full details arenıt available yet, the just-announced eZ80 intends to fast-forward the Z80 architecture up to current specifications and standards.

The chip can mimic three CPUs: the Z80, the ı180 (including its MMU architecture), and a new variant that incorporates a 24-bit ALU and features linear addressing of a 16-MB address space. The former modes are strictly upward object-code compatible with their existing 8-bit brethren, while the latter includes new registers and instructions that extend operations to 24 bits. Multiple virtual 8-bit machines can reside in the 16-MB address space and a mixed mode dynamically switches between existing Z80 and ı180 and new eZ80 native software.

I donıt have any details, but Zilogıs claims of up to 80 MIPS would be consistent with a modern pipelined design. Actual performance would likely be derated somewhat by practical concerns, such as branch penalty and memory bottleneck. Nevertheless, itıs clear the combination of modern architecture and higher clock rate can deliver significant performance, especially with the addition of an optional MAC engine featuring 16 ı 16 multiply and accumulate with a 40-bit result.

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