Another Kind Of “Bare Metal”: 6502 Computer Powers RPN Calculator

[Mitsuru Yamada] states that one of the goals for this 6502 computer build was to make it strong enough to survive real-world usage. In that regard alone we’d call this a success; the die-cast aluminum enclosures used a little blast from the past and lend a nice retro industrial look to the project. The main chassis of the computer fairly bristles with LEDs and chunky toggle switches for setting the data and address busses. The interior is no less tidy, with the 6502 microprocessor — date code from 1995 — and associated support chips neatly arranged on perf board. The construction method is wire wrapping, in keeping with the old-school look and feel. Even the hand-drawn schematic is a work of art — shades of [Forrest Mims].

As for programming, this machine is as low-level as it gets. Nothing but 6502 machine language here, entered manually with the toggle switches, or via an externally programmed ROM. The machine can only address 1k of memory, a limit which the code to support the RPN calculator add-on [Yamada] also built brushes up against, at 992 bytes. The calculator keypad has a 20-key matrix pad and an eight-digit dot-matrix LED display, and can do the four basic operations on fixed-point binary-coded decimal inputs. The brief video below shows the calculator in action.

We love the look of this build and we’re eager to see more like it. We’ve seen a ton of 6502 builds from discrete chips lately, and while we love those too, it’s nice to see one of the big old DIPs put back in action for a change.

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Riding The Nostalgia Train With A 6502 From The Ground Up

In the very early days of the PC revolution the only way to have a computer was to build one, sometimes from a kit but often from scratch. For the young, impoverished hobbyist, leafing through the pages of Popular Electronics was difficult, knowing that the revolution was passing you by. And just like that, the days of homebrewing drew to a close, forced into irrelevance by commodity beige boxes. Computing for normies had arrived.

Many of the homebrewers-that-never-were are now looking back at this time with the powerful combination of nostalgia and disposable income, and projects such as [Ben Eater]’s scratch-built 6502 computer are set to scratch the old itch. The video below introduces not only the how-to part of building a computer from scratch, but the whys and wherefores as well. Instead of just showing us how to wire up a microprocessor and its supporting chips, [Ben] starts with the two most basic things: a 6502 and its datasheet. He shows what pins do what, which ones to make high, and which ones get forced low. Clocked with a custom 555 circuit that lets him single-step and monitored with an Arduino Mega-based logic analyzer, we get a complete look at the fetch and execute cycle of a simple, hard-wired program at the pin level.

This is one of those rare videos that was over too soon and left us looking for more. [Ben] promises a follow-up to add a ROM chip and a more complex program, and we can’t wait to see that. He’s selling kits so you can build along if you don’t already have the parts. There seems to be a lot of interest in 6502 builds lately, some more practical than others. Seems like a good time to hop on the bandwagon.

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Getting To Know Every Bit Of An ATtiny13

We recently heard it said of a hacker who pulled off a particularly nice VGA hack on an 8-bit microcontroller: “He knows all the bits, personally.” High praise, indeed. If you want to get on a first-name basis with a ton of transistors, then have a look at [Heinz D]’s Vacation Course in ATtiny13 Assembler (original in German, translated into English by robots here).

But be warned, this isn’t the easy way to learn AVRs. Not content with simply stripping away every layer of abstraction, this month-long “course” in AVR assembly starts off programming the chip initially with just two pushbuttons in its native machine language of high and low voltages. But still, especially if you can get a few assignments done in one sitting, you’re writing in the relative splendor of assembly language and uploading code with a proper programmer before long, because there’s a real limit to how much code one can toggle in before going mad.

There’s a beautiful minimalism to this entirely ground-up approach, and maybe it’s an appropriate starting point for learning how the machine works at its lowest level. At any rate, you’ll be able to lord it over the Arduino crew that you were able to get blink.ino up and running with just a pair of mechanical contacts and a battery. Real programmers

And once you’ve mastered AVR assembly language, you can recycle those two buttons to learn I2C or SPI. What other protocols are there that don’t have prohibitive timeouts? What’s the craziest code that you’ve ever entered bit by bit?