The 8721 PLA, or programmable logic array, was one of the chips that had to be invented to make the Commodore 128, the last of the 8-bit computers that formed the leading edge of the early PC revolution, a reality. [decided to reverse engineer it, to see what the C-128 designers had in mind back in mid-1980s.
] got a hold of one of these chips and
PLAs were the FPGAs of the day, with arrays of AND gates and OR gates that could be connected into complex logic circuits. [Johan]’s investigation started with liberating the 8721 die from its package, for which he used the quick and easy method favored by [CuriousMarc]. The next step was tooling up, as the microscope he was using proved insufficient to the task. Even with a better microscope in hand, [Johan] still found the need to tweak it, adding one of the new high-quality Raspberry Pi cameras and motorizing the stage with some stepper motors and a CNC controller board.
With optics sorted out, he was able to identify all the pads on the die and to find the main gate array areas. Zooming in a little further, he was able to see the connections between the matrices of the AND and OR gates, which makes decoding the logic a relative snap, although the presence of what appears to be an output block with latching functions confounds this somewhat.
The end result is a full Verilog HDL file that reflects the original 8721 logic, which we think is a pretty neat trick. And we’d love it if our own [Bil Herd] could chime in on this; after all, he literally designed the C-128.
Drone racing comes in different shapes and sizes, and some multirotor racers can be very small indeed. Racing means having gates to fly though, and here’s a clever DIY design by [Qgel] that uses a small 3D printed part and a segment of printer filament as the components for small-scale drone racing gates.
The base is 3D printed as a single piece and is not fussy about tolerances, meanwhile the gate itself is formed from a segment of printer filament. Size is easily adjusted, they disassemble readily, are cheap to produce, and take up very little space. In short, perfect for its intended purpose.
Races benefit from being able to measure lap time, and that led to DIY drone racing transponders, complete with a desktop client for managing the data. Not all flying is about racing, but pilots with racing skills were key to getting results in this Star Wars fan film that used drones. Finally, those who still feel that using the word “drone” to include even palm-sized racers is too broad of a use may be interested in [Brian Benchoff]’s research into the surprisingly long history of the word “drone” and its historically broad definition.
Logic gates are the bricks and mortar of digital electronics, implementing a logical operation on one or more binary inputs to produce a single output. These operations are what make all computations possible in every device you own, whether it is your cell phone, computer, gaming console etc. There are myriad ways of implementing logic gates; mechanically, electronically, virtually (think Minecraft), etc. Let’s take a look at what it takes to create some fun, out-of-the-ordinary gate implementations.
Continue reading “Make Logic Gates Out Of (Almost) Anything”
Although it’s not the best way of understanding computers, most people tend to imagine electronic devices as black boxes filled with magic and blue smoke. Even microcontrollers, the most fundamental means of computation, are treated like little black plastic centipedes with metal legs. In a series of blog posts, [Andrew Gibiansky] is tearing down the walls of obfuscation and illuminating the world of transistors, gates, and FPGAs.
The first blog post goes over the idea of electronic circuits as a waterfall; a positive voltage is a reservoir on a mountain top and ground is sea level. This idea is extended to the lowly transistor acting as an electronic switch, able to turn a circuit on and off.
Continuing on to logic gates, [Andrew] covers the NOT, AND, and OR gates before moving on the flip-flops and SRAM. These can, of course, be modeled in Verilog and VHDL – programming languages that abstract the world of transistors and gates into a much more human-readable form.
[Andrew] is far from done with his series of blog posts, but judging from his work so far it seems to be a great resource for untangling the obtuse concepts of gates and memory into the coherent design of a computer.