Doubling The CPU Speed Of The TRS-80 Model 100 With A Mod Board

The TRS-80 Model 100 was released in 1983, featuring an 80C85 CPU that can run at 5 MHz, but only runs at a hair under 2.5 MHz, due to 1:2 divider on the input clock. Why cut the speed in half? It has a lot to do with the focus of the M100 on being a portable device with low power usage. Since the CPU can run at 5 MHz and modding these old systems is a thing, we got a ready-made solution for the TRS-80 M100, as demonstrated by [Ken] in a recent video using one of his ‘daily driver’ M100s.

This uses the board design from the [Bitchin100] website, along with the M100 ROM image, as one does not simply increase the CPU clock on these old CPUs. The issue is namely that along with the CPU clock, connected components on the CPU bus now have to also run at those speeds, and deal with much faster access speed requirements. This is why beyond the mod board that piggybacks on top of the MPU package, it’s also necessary to replace the system ROM chip (600 ns) with a much faster one, like the Atmel AT27C256R (45 ns), which of course requires another carrier board to deal with incompatible pinouts.

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TRS-80 Model 100 Gets 64-Bit CPU And A Very Wide LCD

To say the TRS-80 Model 100 was ahead of its time would be something of an understatement. It had a high-quality mechanical keyboard, phenomenal battery life, plenty of I/O and expansion capabilities, and was actually small and light enough to easily carry around. While its layout might seem to be a bit dated to modern eyes, there’s little debate that it was one of the most successful and influential computers in history.

So it’s little surprise that [belsamber] thought the Model 100 might make an ideal platform for his mobile command line work. With a few modifications, naturally. While technically the nearly 40 year old portable could connect to a Linux computer as a simple serial terminal, its outdated and non-backlit LCD leaves a bit to be desired in 2021. But there’s little sense in upgrading the display if he’d still be saddled with the anemic Intel 80C85 motherboard, so he decided to clean house and replace everything.

Once stripped of the original hardware, the Model 100’s enclosure offered up plenty of room for a Pine A64 LTS single-board computer, four 18650 cells, and a 1920×480 ultra-wide LCD. While not a perfect match for the dimensions of the original panel, the new screen is an exceptionally close fit. The keyboard has been left intact, but rather than adding a QMK-compatible microcontroller to the mix, [belsamber] wired the matrix directly into the GPIO of the A64.

While we know some retro aficionados might shed a tear to see an iconic computer get gutted, [belsamber] mentions that nothing will go to waste; the parts he pulled from this machine will serve as spares for a second Model 100 he has in his collection. Besides, given the immense popularity of these machines, they aren’t exactly rare to begin with.

As an aside, we recently saw this same unique display used in a 3D printed desktop computer with distinctively retro-futuristic styling. We didn’t have miniature 4:1 ratio displays on our list of 2021 hardware predictions, but it seems they’re already making a strong showing.

Vintage Speech Synthesizer Croons The Oldies

If you listened to the National Weather Service Weather Radio in the US about 25 years ago, you’ll no doubt remember [Perfect Paul], one of the synthesized voices used to read current conditions and weather forecasts. The voice came from a DECtalk DTC01, a not inexpensive voice synthesizer first made in 1984 that also gave voice to [Stephen Hawking] for many years.

Long obsolete, the DECtalk boxes have a devoted following with hobbyists who like to stretch what the device can do. Some even like to make it sing, after a fashion, and [Michael] decided that making a DECtalk sing “Xanadu”, the theme song from the 1980 [Olivia Newton-John] musical extravaganza, was a good idea. Whether it actually was is debatable, and we’ll take exception with having that particular ditty stuck in our head as a result, but we don’t judge except on the merits of the hack.

It’s actually easy if you have a DECtalk; the song is a straight ASCII file with remarkably concise instructions on which phonemes the box needs to generate. Along with inflection, tone, and timing instructions, the text file looks almost completely unlike English while still somehow being readable. The DECtalk accepts the file over RS-232, which would be easy enough to do with a modern computer, but [Michael] upped his game a bit by using a TRS-80 Model 100 computer as a serial terminal. The synthesized song is in the video below, with the original included for reference by those who didn’t experience endure the late disco-era glory days.

DECtalks seem pretty rare in the wild, so we appreciate this glimpse at what they can do. There are other retro speech synthesizer hacks, though: the simulated walnut goodness of the Votrax and the MicroVox come to mind, as does the venerable TI Speak and Spell.

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The TRS80 Model 100 Gets A Brain Transplant

We’ll forgive you if you were busy in the ’80s, and missed the TRS80 Model 100. It was a portable version of the original, ran on four AA batteries, and even had an integrated acoustic coupler which proved handy for workers on the go. However, time is rarely kind, and [Trammell] had come across a non-functional example for just $20. It was time to bring this relic screaming into the modern age.

The motherboard was toast, so [Trammell] decided to wire up a Teensy++ directly to the Hitachi HD44102 display driver chips. Being an older LCD, the display needed a negative bias voltage, so a few diodes, capacitors and a PWM line stepped in to create a charge pump. There was no character generator on board, so the heavy lifting is all handled by the Teensy itself. The keyboard was a simple enough matrix design, so that was wired straight up.

[Trammell]’s work with this iteration got as far as acting as a USB serial terminal, and there was some work done on VT100 emulation. However, according to Twitter, the next stage involves an iCE40 FPGA and some music with which we’re altogether too familiar.

[Trammell] owns a working Model 100, too – employed in some modem experiments, no less.

TRS-80 Model 100 Goes Cellular

There are a few old products that have rabid fan bases, and the TRS-80 Model 100 is one of those. Depending on your point of view it’s either a small laptop or a large organizer, but in 1983 it was the ultimate computer on the go. The $1100 version had a whopping 8K of memory and the LCD screen showed 8 lines of 40 characters in glorious monochrome. One cool feature was the built-in 300 baud phone modem, which [Trammell Hudson] wanted to try, but he doesn’t have a landline. He tried a VOiP phone, but it wouldn’t wedge into the acoustic couplers well enough. Then he decided to go cellular.

He had already hooked up an old ITT 500 series dial phone to an Adafruit Fona ceullar board. He even has Teensy software to decode the dial, drive the dial tone and otherwise make the phone work. This time he hooked a handset up through a headset jack.

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DIY 6502 Laptop Computer Looks And Works Great

Over the years, we’ve seen a lot of DIY retro computers, but [Dirk Grappendorf] has created one of the most polished looking 6502 systems to date. His battery-powered portable machine utilizes a 4 line by 40 character LCD, and a modified USB keyboard. Cover all that in a slick 3D printed case, and you have a machine that reminds us quite a bit of the venerable TRS-80 Model 100.

homecomputer-6502-v8-via-bread[Dirk] has some great documentation to go with his computer. He started with a classic MOS 6502 processor. He surrounded the processor with a number of support chips correct for the early 80’s period. RAM is easy-to -use static RAM, while ROM is handled by UV erasable EPROM. A pair of MOS 6522 Versatile Interface Adapter (VIA) chips connect the keyboard, LCD, and any other peripherals to the CPU. Sound is of course provided by the 6581 SID chip.  All this made for a heck of a lot of wires when built up on a breadboard. The only thing missing from this build is a way to store software written on the machine. [Dirk] already is looking into ways to add an SD card interface to the machine.

homecomputer-6502-final-4The home building didn’t stop there though. [Dirk] designed and etched his own printed circuit board (PCB) for his computer. DIY PCBs with surface mount components are easy these days, but things are a heck of a lot harder with older through hole components. Every through hole pin and via had to be drilled, and soldered to the top and bottom layers of the board. Not to mention the fact that both layers had to line up perfectly to avoid missing holes! To say this was a lot of work would be an understatement.

homecomputer-6502-final-5[Dirk] designed a custom 3D printed case for his computer and printed it out on his Ultimaker. To make things fit, he created his design in halves, and glued the case once printing was complete.

If awesome hardware and a case weren’t enough, [Dirk] also spent time designing software for the machine. He wrote his own abbreviated BASIC interpreter along with several BASIC programs. You can find everything over on his GitHub repository.

We always love writing up well-documented, and just generally awesome projects like [Dirk’s]. If you know of any retro computers like this one, drop us a tip!

[Thanks MicroHex!]

Building A New Motherboard For A TRS-80

Trash80

The TRS-80 Model 100 was an amazing piece of kit when it was released. Able to run for a week with just four AA batteries and smaller than some laptops today, this portable version of the TRS-80 saw action with war correspondents covering the Falklands invasion. A pedigree a MacBook Pro will never be able to live up to, it seems.

[Hudson] picked up a non-functioning Model 100 with the express goal of replacing the 30-year-old electronics inside with an updated motherboard – and also pull up our retro site in the process. Armed with a Teensy++, [Hudson] pried open his ancient computer and set to work interfacing the display and keyboard to his AVR dev board.

The LCD display in the Model 100 has a resolution of 240×64, driven by ten Hitachi HD44102 display drivers. Each of these display drivers are responsible for the pixels in a 50×32 rectangle on the screen and are interfaced with a 30-bit wide bus consisting of chip select lines, and 8-bit data bus, and a few other random control lines. [Hudson] plugged this 30 pin header into his Teensy++ and after a bit of ingenuity regarding the strange electrical requirements of the LCD, was able to control every pixel on this 30-year-old display.

The next order of business was interfacing the keyboard with a modern microcontroller. The keyboard is laid out in a normal matrix, but with a few oddities: characters like ~, |, and curly brackets aren’t present on the Model 100. After working these problems out, [Hudson] set to work on a VT100 terminal emulator. This allowed him to run vi and lynx, enabling him to pull up the Hackaday retro site in a wonderful forty-column text mode.

Future improvements to this redesign include designing a proper PCB to replace the current protoboard design. The original Model 100 included a text editor and programming language, and adding a Forth implementation isn’t out of [Hudson]’s grasp. It’s an awesome build, and an excellent improvement that will allow [Hudson]’s Trash-80 to see another 30 years of use.