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Imagesource: https://hackaday.io/
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Admittedly, when we talk about old CPUs, it's mostly about the 6502 or the Z80. Guilty. But truth be told, the 6502 usually gets the preference. This needs to be changed urgently, and therefore we are super grateful for the hint and work of one of our faithful readers Paolo Amoroso. Paolo is more in the Z80 camp and has recently assembled the Z80-MBC2. This beautiful machine is the successor of the Z80-SBC (single board computer), brings an SD card reader and 128kB banked RAM, so besides CP/M 2.2 also CP/M 3, QP/M and Collapse OS can be run on the box. But what do you do after the soldering iron has cooled down and you have cured the resulting burns? 🩹 Paolo answers this very question with an interesting series of blog posts. A first look at hardware and software, building a first demo in assembly, a serial connection to chromeOS and an alternative for program upload are the first topics documenting Paolo's journey. More to come. For those who have always wanted to enter Z80 territory, both the device and especially Paolo's article are highly recommended.
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Imagesource: https://scribd.com/
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If you think soldering irons are the devil's work (Hello), don't want to maltreat pieces of cable and your own fingers with a wire stripper, but still feel like designing digital circuits, there are options. LogiSim in its different flavors or the excellent alternative Digital by Helmut Neemann will get you surprisingly far. Even larger projects are no problem thanks to the abstraction capabilities via modules. But if you want to go back to the hardware world, both tools are not always directly usable, even though they provide Verilog generated descriptions of your design. And Verilog alone generates real joy, because you can describe very complex digital circuits very quickly with very little code. In short, there's no getting around Verilog if you're serious about building something and to bringing it to life on an FPGA or ASIC afterwards. One of the best books on the subject comes from Samir Palitkar. The first edition of "Verilog HDL" dates back to 1993, but has been updated again and again by the author. Paperback and hardcover versions are available (in some countries) from Amazon, but here and here you find digital versions. To be fair, those who want to support Samir put some colorful bills on the Amazon sales counter. The book assumes only basic knowledge, and is an excellent choice to get started with Verilog. Definitely reading material for a hot summer! 😎
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One of the reasons why vintage 8-bit CPUs like the MOS 6502 are still so popular (and manufactured) today, is that they are so approachable. The instruction sets of these chips are usually so small, that you can write machine code almost by hand, and just understand the thing as a whole. But oftentimes it happens, that after building your own 8-bit machine, you end up only implementing some simple experiments. You add two 8-bit numbers, maybe implement a 16-bit addition with carry and then ...🥱 But actually it gets really interesting, when you start coding the axiom tree of mathematics. At least a part of it. And what are the obvious candidates if your hardware can add and subtract? Right, multiplication and division. Neil Parker's writeup on the subject is as competent as it is interesting. And if you're in the mood to finally breathe a little more life into the DIY build on your desk in the coming days off, you'll definitely get a taste for it again here!
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Imagesource: https://unsplash.com/
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For all those who are not yet so deep into the matter, and would not yet be able to put a Turing-complete machine on paper (or breadboard or PCB), the following is certainly interesting. Jessica Card who is involved in the Hack Club, has put together a wonderful tutorial about assembly. Some Assembly Required not only introduces you to the topic without the necessity of any prior knowledge. There are very practical examples of x86, RISC-V and 6502 assembly, where even die-hards can learn a thing or two. Excellently summarized in a GitHub repo, and thanks to the work of 13 Contributors a really good source of knowledge. Thanks for that! 🙏
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