Issue 153 April 2003
Test-Driving the Z8

Start • The Z8 Kit • Bring Up The Software • The Z8 Goes 10/100 Mbps • Get One • Sources and PDF

It wasn’t too long ago when we were all praising the king (the Z80) in his court (the Tandy computer center). Radio Shack and Tandy had suddenly taken the market with the introduction of their TRS-80 PC line. Running at just below its 2.5-MHz clock limit (2.03 MHz), the TRS-80 Model 3—equipped with a Z80, 16 KB of RAM, a version of BASIC in 14 KB of ROM, a monochrome video display, and a floppy drive—cost you about $1000. You could walk into just about any Radio Shack and walk out with one in hand.

I remember the "computer specialist" at my store once said, "Man, the new 4-MHz models are coming out soon. I don’t know if our software can keep up." He drove a Cadillac; and yes, I was one of those sales-floor guys at Radio Shack. I was known as "The Wizard" in those days. It’s amazing what knowing the resistor color codes can do for your career. One time, when the boss saw that I could operate the store demo, he put the TRS-80 in the window in an attempt to attract the attention of passersby by having me play games during my downtime. And, for you guys and gals working today’s computerized Radio Shacks, we would write all of our tickets by hand, including the big ones for TRS-80 Model 3s.

For those of us (employee or customer) who couldn’t afford a shiny steel-gray TRS-80 Model 3, there were the Z80 micro, 2716 ultraviolet-erasable EPROM, 74LS04-driven clock generator, 2-KB chunk of relatively expensive static RAM, 74LS138 address decoder, and 74LS244 and 74LS373 for I/O and Z80 assembler code. Back then about the only thing that a homemade Z80 embedded system had in common with Radio Shack was the perf board it was built on.

I can recall purchasing a Z80 cross assembler for my PC for $450. (Yeah, I really wanted it bad, didn’t I?) The idea was to be able to write the Z80 source code on my PC and assemble it with the PC so that I could load the resulting Z80 object file directly into my EPROM programmer, which was also attached to my PC via a proprietary plug-in card. Using this configuration, I could actually write the Z80 mnemonics and have the PC do the compiling and linking work instead of hand-assembling hexadecimal Z80 machine instructions. Boy, I had arrived! At that time, my Z80A projects were sometimes running with a clock that was as fast as my PC’s clock.

Today, for as little as $49 (at the time of this writing), you can purchase a Z8 Encore! development kit containing a 20-MHz, Z80-like device (i.e., Z8F6403) running at 18.432 MHz with 64 KB of embedded flash memory to replace the EPROM and the ultraviolet EPROM eraser, 4 KB of native SRAM (which eliminates that external SRAM IC and address decoder), and most of the goodies found on the original Z80 (e.g., DMA, timers, and so on). In fact, the Z8 Encore! microcontrollers sport their own set of on-chip UARTs and A/D converters; however, the dynamic RAM refresh feature of the original is nowhere to be found on the new models.