One of the PCB projects involved being held in the author's hands - a large-ish green board, with two Pi Picos visible on it

RP2040 And 5V Logic – Best Friends? This FX9000P Confirms!

April 5, 2023 by Arya Voronova 26 Comments

Over the years, we’ve seen some modern microcontrollers turn out to be 5V-tolerant – now, RP2040 joins the crowd. Half a year ago, when we covered an ISA card based on a Pi Pico, [Eben Upton] left a comment saying that RP2040 is, technically, 5V tolerant for GPIO input purposes. The datasheets don’t state this because the reality of 5V tolerance isn’t the same as for natively 5V-tolerant chips – for instance, it doesn’t extend all the way to 5.5V for it to be ‘legally’ 5V-tolerant, as in, what 5V tolerance typically means when mentioned in a datasheet.

Having read that comment, [Andrew Menadue] has set out to test-drive the RP2040 GPIO capabilities, in a perfectly suited real-world scenario. He’s working with retro tech like Z80-era computers, using RP2040 boards for substituting entire RAM and ROM chips that have died in his FX9000P. Not only do the RP2040-driven replacements work wonders, using RP2040 boards also turns out to be way cheaper than sourcing replacements for chips long out of production!

Previously, [Andrew] used level shifter chips for interfacing the RP2040 with 5V systems, but he’s rebuilt a few designs of his without level shifters for the sake of this experiment. Now, he reports that, so far, those boards have been running long-term without problems. Together with [Eben]’s comment, this instills confidence in us when it comes to our RP2040 forays and 5V inputs.

There are a number of important caveats to this, that you should read up on. Some major points – certain GPIOs (like ADC ones) can’t take it, the GPIOs aren’t 5V-tolerant when set to output, and you shouldn’t feed the GPIOs 5V when the RP2040’s VDDIO is not powered up. [Andrew] points out one such case himself – one board of his has shed all level shifters except for the 8-bit address bus, which is driven by either the CPU or the RP2040 at different times, and that would result in 5V on an output-set GPIO when contention happens. All in all, if you’re working with 5V logic and your application is more hacking than business-critical stuff, you can shed the level shifters, too.

Continue reading “RP2040 And 5V Logic – Best Friends? This FX9000P Confirms!” →

Upgrade Your Voodoo With More Memory

April 4, 2023 by Al Williams 24 Comments

In 1996, the 3Dfx VooDoo VGA chipset changed computer graphics forever. Because of the high cost of memory, most of the boards had only 4 MB of memory — which seemed a lot back then. However, the chipset could actually handle up to 8 MB. [Bits and Bolts] couldn’t stand that his board only had 4 MB, so he did what any good hacker would do: he figured out how to add the missing memory!

The mod has been done before using the “piggyback” technique, where you solder the new RAM chips on the old chips and bend out a few pins out to directly wire them to chip selects elsewhere on the board. [Bits and Bolts] didn’t want to try that, so instead, he developed a PCB that slips over the chip using a socket.

Continue reading “Upgrade Your Voodoo With More Memory” →

An expansion board with two 8-bit ISA slots plugged into a Sharp laptop

New Expansion Module Brings Standard Slots To Ancient Laptop

April 4, 2023 by Robin Kearey 10 Comments

Upgrading and repairing vintage laptops is often a challenge — even if their basic hardware is compatible with ordinary PCs, they often use nonstandard components and connectors due to space constraints. The Sharp PC-4600 series from the late 1980s is a case in point: although it comes with standard serial and parallel ports, the only other external interface is a mysterious connector labelled EXPBUS on the back of the case. [Steven George] has been diving into the details of this port and managed to design a module to turn it into a pair of standard ISA ports.

Apparently, no peripherals were ever released for the EXPBUS port, so reverse-engineering an existing module was out of the question. [Steven] did stumble upon a service manual for the PC-4600 however, and as it turned out, the connector carried all the signals present in an 8-bit ISA bus. Turning it into something useful was simply a matter of designing an adapter board with the EXPBUS connector on one side and regular ISA slots on the other.

The board also has an external power connector, to avoid overloading the laptop’s internal power supply, as well as a couple of buffer capacitors to smooth out the power rails. [Steven] tested the expansion board with a network adapter and a sound card, and it appears to be functioning well. It should be noted that only the +5 V power rail is available by default, so if any cards need +12 V or any negative rail, those should be provided externally.

Gerber files for this project are available on [Steven]’s website, so if you’ve got one of these machines lying around, now might be the time to upgrade it. This isn’t the first expansion for the PC-4600 series that [Steven] developed, either: he also designed an external floppy drive adapter that should ease data transfer with other PCs.

It’s great to see how the hacker community keeps classic portables like this one alive: one day it might also need a broken screen replaced or a dodgy power supply repaired.

CP/M 6502-Style

April 4, 2023 by Al Williams 8 Comments

There are projects you create to share with the world, but there are also those you do just because you want something for yourself. Lucky for us, [Dietrich-L]’s 30-year-long project to create CPM-65, a CP/M-like OS for the 6502, has become both.

[Dietrich-L] does admit that the documentation is “sparse” and “for my personal needs.” Still, the OS has most of what you’d expect and runs well on the target system, a heavily-modified Elektor Junior with 57 kB of RAM. The disk structure is compatible with CP/M, although the Transient Program Area (TPA) apparently starts at $200, which is a bit different from a typical CP/M. Apparently, the system uses some low memory which necessitated the relocation. Just in case you were hoping, CPM-65 doesn’t emulate an 8080 system, so you can’t run normal CP/M programs. You just get a similar operating environment and tools.

The 31 commands listed include an assembler, BASIC, Forth, an editor, and some disk tools, along with a debugger. Xmodem is available, too. Everything is written in assembly for the CPM-65 assembler, so bootstrapping could be an issue if you need to make any changes.

Speaking of changes, there is some documentation in the docs sub-directory, including the layout of [Dietrich-L]’s system, which would be handy if you were trying to run this on your own hardware. You’ll also find basic commands for the editor, details of the assembler, and some other documents.

[Dietrich-L] notes that he was unaware when he started the project that there were other similar projects. DOS/65 (which has a port for the Commodore 64), OUP/M (which hasn’t been updated since 1983), and CPM65 (apparently no relation, but very impressive), which appeared in 2022.

If you need a 6502 computer, grab a breadboard, although adding the disk drive is an exercise left to the reader. Or, grab an FPGA but expect more work.

Thanks [Stephen Walters] for the tip!

Apple Never Gave Them USB. Now, They’re Getting It For Themselves

April 1, 2023 by Jenny List 14 Comments

These days we use USB as a default for everything from low-speed serial ports to high-capacity storage, and the ubiquitous connector has evolved into a truly multi-purpose interface. It’s difficult to believe then, that the first Apple Mac to be designed with a USB interface was shipped without it; but that’s the case with 1997’s grey Power Mac G3.

On the personality board are all the footprints for a single USB 1.1 port, but USB-hungry Apple fanboys had to wait for the translucent iMac and later G3 before they had a machine with the parts fitted. [Croissantking] is righting that particular wrong, by piecing together the missing Apple circuit using parts from contemporary cards for PCs. Over a long forum thread there are a few teething problems, but it certainly seems as though grey G3 owners will soon be able to have reliable USB upgrades.

If omitting USB from a 1997 Mac seems unexpected, it’s as well to remember how slow the first USB versions were. At the time SCSI was king in the high-speed peripheral world, and USB seemed more appropriate as a replacement for Apple Desktop Bus and the serial port. Even when they embraced USB they were reluctant to follow the standards of the PC world, as we remember finding out when for curiosity’s sake we tried swapping the mice and keyboards between an iMac and a Windows PC. We have USB’s success to thank for releasing Mac users from a world of hugely overpriced proprietary peripherals.

If you fancy hacking a ’90s PowerMac, make sure you get one that works.

Thanks [Doug] for the tip.

Working With Old High-Voltage EPROMs Is Fussy

March 31, 2023 by Zoe Skyforest 19 Comments

EPROMs, those UV-erasable memory chips of the 80s and 90s, once played a crucial role in countless electronic devices. They’ve become relics of a bygone era, but for enthusiasts of vintage electronics, the allure of these light-sensitive devices remains strong. Today, we’re diving into [Kevin Osborn]’s nostalgic journey as he uncovers the secrets of old EPROMs loaded with Atari 7800 code.

[Kevin] used to work at General Computer Company, which produced the Atari 7800 and several games for the system. Thus, he had a handful of old carts and development EPROMs sitting up in his attic along with an old console. Recently, he decided to try and uncover what was on the EPROMs and begun an investigation. They wouldn’t run in his Atari, and he quickly realized why: the EPROMs weren’t cryptographically signed, so the system wouldn’t load them. Continue reading “Working With Old High-Voltage EPROMs Is Fussy” →

EPROM Does VGA

March 29, 2023 by Al Williams 16 Comments

If you wanted to create a VGA card, you might think about using an FPGA. But there are simpler ways to generate patterns, including an old-fashioned EPROM, as [DrMattRegan] points out in a recent video.

Generating video signals is an exercise in periodicity. After all, an old-fashioned CRT just scans at a certain horizontal frequency and refreshes the entire screen each time it starts over. VGA is made to drive this technology. An EPROM chip can easily generate repeating patterns when driven by a counter at a known frequency.

As you might expect, there were a few software glitches to work out, but in the end, the circuit did its job, displaying a fixed image on a VGA monitor.

If you haven’t run into [Matt] before, he has a complete series on how he built a “wire-by-wire” Apple II clone. We will warn you, though. Don’t click on the link unless you have some spare time. The 18 videos take over two hours to work through, but there is some beautiful prototyping and a lot of good information in them.

You can go even lower tech for a VGA card, if you like. Just try not to look like this breadboard.

Continue reading “EPROM Does VGA” →