Energy Star -- Paleotechnology style!

A while back, I realized that the Z80 was drawing (relatively speaking) a lot of power. I know modern CPUs can both crunch your numbers and cook your dinner; the Intel Core i7 datasheet specifies a maximum of 145 AMPS of current. (I don't think my car's starter motor draws that much, some days.)

The Z80, though, being from the ancient glory days of yore when CPUs didn't even require a heatsink, let alone sophisticated cryogenics, didn't really strike me as a power hog. In fact, the version the DrACo/Z80 uses is CMOS-based (for static clockability) -- it couldn't be drawing some 700 milliamps of power all on its own, could it?

No, as it turns out. The Z80 itself is quite efficient. The 74LS245 buffer chips, on the other hand, draw 40 or 50 mA apiece, even when doing absolutely nothing. They just sit there and get warm! "Low-power Schottky," my paleotechnological posterior!

A quick look online turned up the drop-in replacement 74HCT245 version, which is much more power-friendly. (These only draw a few microamps when idle.) The results speak for themselves...



Much more Earth-friendly! (...and now the computer can be run from a USB port or from NiMH batteries. Whether the Department of Security Theater would let me on a plane or on Amtrak with it is most likely another story, though.)

I'm also experimenting with removing the '245 chips connecting the Z80 to the bus. It works well enough to do the Prime Number program, but may not be as stable for high-speed operation. More on this later (time permitting).

I'm still here...

...I've just been busy working on some really cool paleotechnology projects. Dr. Rosen came across an article about a microprocessor course built around students creating their own 8086-based computer. He asked me what I thought about it -- and my first thought was "Can I sign up, even though I'm not an undergrad?"

Since then, I've been working on coming up with a working computer design that EET students could have a chance of building in one ten-week term. (Drexel is on the quarter system.) Since nearly all modern PCs are based on x86 architecture, Dr. Rosen suggested that, like the course described in the article, we design the course around an 8086 computer. Here is the design. (Caveat lector: I haven't completely built this one -- let alone debugged the design. It almost certainly has multiple bugs. Consider it pre-alpha.)

Upon further reflection, Dr. Rosen pointed out that this design (rather complex, not to mention costing perhaps $250 in parts) was probably too ambitious for a one-term undergrad class. He asked what I thought we could do to simplify the design. I pared it down, removing the RS232 subsection and making a few other minor changes -- but it became apparent to me that an 8088-based design would be significantly simpler and less expensive. Continuing this line of reasoning, I figured that a Z80-based design would be simpler still. (The Z80-based Timex-Sinclair 1000, after all, uses a total of only four ICs.)

Here is the Z80-based design. (Again, this has not yet been completely built, let alone debugged. Should we go with this design and build it, I will post complete plans here.)