Issue
139 February 2002
eZ
Embedded Web
by
Tom Cantrell
In
With the Old and the New
For
those of you who missed my earlier article, let’s take
a quick and eZ refresher. The challenge posed by the eZ80
was to carry forward the happy days’ sentiment for the
Z80 while significantly upgrading under the hood. Sounds
easy, but it isn’t. Nevertheless, I reported in "eZ
Does It" that I thought Zilog had done a remarkably
good job, at least on paper. See for yourself in Figure
1.
|
|
Figure
1—We’re going back to the future. The eZ80 carries
the legacy of the Z80 into the 21st century. |
Architecturally,
it’s always hard to make a chip that is both the same
and better than its predecessor. This is especially true
when it comes to getting past the 64-KB address space
barrier characteristic of practically every popular 8-bit
chip. Zilog finessed this well with their dual-mode short
(16-bit addresses compatible with Z80) and long (24-bit)
addressing scheme.
Under
the hood, the eZ80 is hopped up with a pipelined, 50-MHz,
24-bit ALU core. Yes, there are wait states required for
off-chip memory to consider, but it’s still much faster
than its predecessor and most 8-bit chips. There’s even
a high-performance 32-bit MAC unit that allows the chip
to do double-duty as a DSP.
Popularity
of the Z80 had as much to do with the add-ons it worked
with, the venerable SIO, CTC, PIO chips of yore. Even
by today’s higher integration standards, the eZ80 holds
its own with fancy serial parts (including asynchronous,
I2C and SPI), half a dozen timer/counter channels, a burst
and cycle steal DMA controller, a wait chip select state
generator,and built-in debug logic.
Although
not a single-chip MCU, the 8 KB of on-chip 1-clock code
and data-capable SRAM (not to mention the extra 1 KB that
comes with the MAC unit) is enough to handle the RAM needs
for a lot of embedded applications. Clever designers will
put the small portion of their code and data that truly
needs top speed there. Combining the eZ80 100-pin QFP
with a single external EPROM or flash memory chip makes
for a tidy yet powerful two-chip solution.
