Author: Ira

KiwiSinceBirth has released v2.0a of his redesigned Model I motherboard. He reports the following changes:

This project is an upgraded / evolved TRS-80 Model 1 main board replacement. It was designed to provide a reliable, compact, and modern replacement, removing some limitations of the original 1970’s product, while still remaining faithful to the original technology (i.e. no emulation)

v2.0a provides significant improvements in video, not only does it use dual port RAM for snow free video, but it changes the video sync generation circuit bringing back the picture adjustment controls not present in V1. Also supported is software switchable fonts, for alternate languages or other graphics. Other major features added to the board include an audio amplifier for a small speaker (which can be mounted on the board), Alpha Joystick port compatible with most software, and ability to mount a modern clock oscillator. Have added about 10 new config jumpers/settings in support of new features. V1 is still fully supported including a separate build guide. Not forgetting Supermem bank RAM and internal FreHD

New Features

• Dual port video SRAM, reducing contention (snow) issues with shared CPU access.
• Onboard Audio amplifier utilising small class D module, with space for PCB speaker
• Alpha Joystick port with header to connect 9 Pin DB9 Connector
• Changed crystal oscillator to parallel resonant circuit based on 74HCU04 chip, which is pin compatible with a Full Can (DIP14) oscillator.
• New Video sync generation circuit, including Horizontal and Vertical Position.
• Improved support for RGBtoHDMI by exposing HSYNC on Video DIN socket
• Added Tim Halloran’s no-chip VBLANK modification, for improved video updating.
• Added Jumper (JP16) to allow main Reset button to function as full CPU reset.
• Can configure either RAM or ROM to occupy the 12kB to 14kB address space in memory.
• Added support for EEPROM in circuit writing (requires software support).

Changed Features

• The Video DIN socket now has Jumper (JP19) to disable external power
• Added PCB reset button (SW11) to allow full reset during diagnostics
• CPU speedup offer fast speed as 5.3 (default 3.55) mhz via jumper (JP17)
• Added Power LED indicator (D1) near to the main power switch.
• Fixed issue with TEST signal immediately disconnecting CPU from BUS – Credit Marcel Erz
• Fixed Issue with Bus control for interrupt Mode 0 and 2 where external device places data on bus
• Added (back) software character set control (Port FF Bit 7), as per JP board.
• Changed meaning of SW10-SW13. Now ON => Logic 1, and OFF => 0 (rather than reverse)
• RAM is configurable from $48k (default) down to 16k for compatability with external RAM.

Minor Improvements

• Moved main 10.6Mhz oscillator to central location, shorter signal paths.
• CPU clock speed selector flip-flop (Z63a) clocked at slowest rate.
• JP10 (and related circuit) used for video frequency was removed.
• Inputs of spare gates are now tied to GND or VCC, with easy trace cuts for future use.
• Added resistor pull-ups on address, data, and control busses, for CMOS stability.
• Added resistor pull-ups on keyboard, prevent issues when no keyboard attached.
• Provided ability to use spare IO pins (CAS and MUX) on IO expansion.
• Moved main power switch (SW1) and socket (J11) closer to other ports, better clearance
• Added several M3 mounting holes for internal expansion board mounting
• Improved (more modern) footprints for C19, C70, Q1, Q2, CR4.
• Replaced several discrete resistors with small resistor packs.
• Fixed multiple issues with small via’s and thermal reliefs on power rails
• Main power Capacitor C101 now has more space for horizontal mounting.
• Improved silkscreen for component identification, and configuration options
• Improved component identification in Bill of Materials
• Major improvement in the Schematic diagram quality.
• Many component designators have changed from V1, so some V1 docs may not be accurate
• Added testpoints to support 3 signals required by SuperMem
• Changed main power capacitor C11 to 470Uf after testing from MSly
• Changed main power switch to discharge C11 (using 100R R14) when switched off
• Keyboard resistor pack RN5 corrected to pull down keyboard data lines.
• Corrections to Bill of Materials, and silkscreen fixes and improvements.

You can find all the information, as well as downloads for the BOM and circuit board, at github.com/kiwisincebirth/TRS-80-MODEL-1-K/tree/main

Update: Claimed

A site visitor (and very frequent contributor) has multiple Model I components that he would like to give away by local pickup only in the Norfolk, Nebraska area.

He lists:

• two monitors
• two expansion interfaces
• three keyboard units (one not working)
• a few floppy drives (condition unknown, but worked a few years ago)
• several DOS manuals, books, and newsletters

If you are interested in picking up that stuff, please contact me and I will pass on your interest.

Well, the first pass of the AI conversion did an OK job, even if it took about a month due to token limits. The problem is that it created 1500 classes because of the number of sessions that had to be used. Instead of it being able to consistently review pages and apply consistent code, even when instructed to re-use old code, it didn’t do a great job.

So I need to make another pass. I have developed, with AI’s help, three main types of code sections – general, columnar, and images. As I move page to page, I have those codes updated as needed. This should bring consistency to the site.

Some of the things about the new design that I absolutely love, is that a simple CSS class added to a catalog entry, email address, or clickable image, just adds a note telling you what you can do with that. This is something I would have used JQUERY for in the past, but CSS3 is pretty awesome! Examples are the little caption on the pictures below; automatically added by CSS.

Anyway, the AI page pass left me with 1500+ CSS entries, and those need to get culled. Well, most of them. It turns out that the new search pages require 450 CSS entries! They are kind of beautiful, so I’m going to leave those alone.

For the rest of the pages, I had Gemini write some Visual BASIC Code to parse every html file, extract every class used, and come up with a display that would show me the class, the code, and the files which use it. I also had to have it let me know about dependencies after a particularly disasterous attempt to globally update the code.

This is a sample of the output.

Here, there is a class used by only 1 page. In this case, it’s because its a typo. But putting that aside, it is my clue as to the next page to edit. I then go through and update the page to use the new classes.

Once that page (or pages) are done, I use WildEdit to search the entire tree for the class.

If it shows no changes made, then I can delete the CSS.

I also had a button prepared that would output the “good” and “bad” css. If I get tired of editing specific pages, but still want to make progress, I use WildEdit to find entries that are on the “bad” page. If there are no results, I can just strike that CSS entry.

So that’s what’s going on now ….

But as of this point, v1 CSS is pretty much gone, so if you see a page (or table) that is broken, let me know!

Between Claude AI and Gemini Pro (but definitely not Gemini Flash), the web site has been updated to new CSS. I have moved prior news into the “old news” pages because WordPress would require me to update each news item individually otherwise.

You can see 2025 news here.

There might be broken CSS when I kill the old CSS. I still have work to do though. Since AI sessions can only be so long, each new session required me to feed in the CSS to date, and I instructed it to re-use as much CSS as it could. Despite that, over 650 new CSS definitions were created; so much for site consistency.