Category Archives: Blog

The TRS-80 Microcomputer RFI Testing Report

By | June 6, 2020

Soon after the release of the TRS-80 Microcomputer in 1977, it became apparent that the computer was emitting significant amounts of RFI (Radio Frequency Interference). A common story at the time is that you could generate primitive sound effects for games by simply placing an AM radio next to the computer. This was a hot topic at the time for many of the new microcomputer manufacturers, including Radio Shack’s competitors TI and Apple, because the FCC soon became involved. Complaints poured in from amateur radio operators and television viewers who were being negatively affected by their neighbor’s new computers. read more

TRS-80 Trash Talk – Episode 33 – The TRS-80 Model 100

By | November 7, 2019

In this episode we review Tandy Assembly 2019. There were lots of additions to the show this year including the new Tech Track. What worked well and what worked not so well? There’s the usual segments on new projects, new acquisitions, listener feedback and the book review. We talk about JetSet which is a flight simulator for the TRS-80 Model II! There’s some discussion about ARCNET, CP/M Plus and floppy disk baking. Then, in our main segment, we talk to TRS-80 Model 100 enthusiast Josh Malone. Josh gives us a great overview and then a detailed rundown of this most famous portable computer. read more

A TRS-80 Network Interface Card

By | February 3, 2019

For the past few months I’ve been working on a project that I’ve been pondering for a long time. If you follow my vintage computing exploits, you know that I get the most satisfaction out of combining retro technology with modern cloud-based systems. This allows me to combine my passion for both vintage and new technology, ie. my hobby and my real-world day-job passions and skills. read more

TRS-80 8 MB Hard Drive Three Wire Fix

By | September 15, 2018

I recently needed to replace the SA1000 hard drive bubble in a Tandy Radio Shack TRS-80 8 MB Hard Disk Drive unit. While I was very familiar with how to do this in one of the later 5 MB or 12 MB hard drives, I had never attempted the procedure on the 8 MB drive. In the end, it was fairly straightforward to replace the bubble, except for dealing with the famous Tandy 3 Wire setup. The 3 Wire Fix has been documented in the past for the smaller 5 MB and later drives, but not for the 8 MB unit. I went ahead and put together that process here.

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Copying Files To and From TRS-80 Model II TRSDOS 2.0

By | May 12, 2018

I’m starting to look into developing a version of TRS-Box for the TRS-80 Model II TRSDOS 2.0 operating system. I already have working versions of TRS-Box for Model II LS-DOS 6 and Model 16 XENIX, but given that TRSDOS 2.0 was the standard Model II operating system, I thought it was important for it to have a working version of TRS-Box.

The first step in developing software using modern tools for any vintage computer is being able to reliably transfer files between the modern and vintage systems.  I plan to do most of the development and cross-assembling of TRS-Box on my  MacBook Pro using OSX.  In this way I can take advantage of a modern editor and assembler which makes development much easier than developing on the Model II.  I love my Model II, but actually using it for software development would

be slow and tiresome today.  So, I need a way of copying the finished program executable to the Model II for testing. The built in serial file transfer utilities of TRSDOS 2.0 are not great, especially for trying to communicate with a modern system. Luckily, we have a copy of the excellent OmniTerm for Model II software in the model2archive.

For the MacBook side, I use the very capable Serial program for all my serial port communication needs. It works well with all of my TRS-80s and operating systems.  Also required are a couple of special serial cables.  I’ve detailed the steps I followed if you would also like to copy files to your Model II running TRSDOS 2.0.  There are many other ways to achieve this goal, but I found this configuration to work well.  The steps should be similar if you are using Linux or Windows with a capable serial communication program.  It is expected that you are familiar with how to use IMD disk images with your Model II.


  1. Set up the physical serial link between the MacBook and the Model II.
    1. You will need a 25 pin RS-232 Null Modem cable on the Model II side.
    2. For the MacBook, use an FT232R compliant USB-Serial adapter.
    3. On the Model II, you need to make sure you use serial port A.  It is recommended that you have another serial device or a serial terminator on port B.  The Model II Owner’s Manual shows how to create a serial terminator.

    Get the Serial program for the MacBook.
    Get OminTerm running on the Model II.  The OminTerm disk is not a bootable disk.  Follow the instructions in the OmniTerm manual to set it up for single disk bootable operation if you only have a single disk drive.  I have multiple disk drives so I use a TRSDOS 2.0 system disk in drive 0 and the OmniTerm disk in drive 1.
    Setup the Serial program on the MacBook.  Go to Terminal->Line Settings.   I have been using 1200 baud, but

    higher baud rates should work as well.  The Model II has a maximum baud rate of 9600.

    1. Baud Rate: 1200
    2. Data Bits: 8
    3. Parity: None
    4. Stop Bits: 1

    Set up the serial port in TRSDOS on the Model II.

    1. SETCOM A=(1200,8,N,1)


    Before you start transferring files, you will want to verify that you have the serial connection properly configured.  You can do this by running the OMNITERM program on the Model II.  You will need to set the baud rate to 1200 by pressing F1 and then “U”. Press F1 again to return to terminal mode.  Once it comes up, anything you type on the Model II should show up in Serial on the MacBook and anything you type in Serial should show up in OmniTerm.  If you have this working, then you are good to start transferring files.  If not, then you need to go back and check your setup.

    Transferring Files

    Now you are ready to start transferring files.  On the Model II we will not be using the OMNITERM program since that is a general purpose terminal program.  It does have ASCII based file transfer support, but we want to use something more reliable than traditional serial ASCII transfer.  On the OminTerm disk there is a program called OMNIXFER.  This is an XMODEM supporting file transfer program.  XMODEM is a reliable serial file transfer protocol developed by Ward Christensen in 1977.

    Once you run OMINXFER, it will ask you if you want to send or receive a file.  Start with sending a file to the Model II so choose R.  Then it will ask for a filename of the file you want to create in which to place the received file contents.  The program will then wait for a file to arrive in XMODEM format on serial port A.

    In Serial, got to File->Send File.  Choose XMODEM as the Transfer Protocol.  Leave the 1K block size unchecked.  Choose the file to send and click Send File.  You should see the file transfer begin between the two machines.

    The process is reversed for getting files from the Model II to the MacBook.  In Serial, go to File->Recieve File.  Select XMODEM and Checksum error checking.  Click on Receive.  Then, on the Model II, run OMNIXFER.  Select to send a file.  Provide the TRS-80 file spec of the file you want to send and the file transfer will start.

    One special consideration needs to be taken when working with TRSDOS 2.0.  Model II TRSDOS treats data files and program files differently.  When you receive a file on the Model II, you will need to run the OMNICONV program on the OmniTerm disk to convert the file to the proper type.  For program files, choose Fixed Length and Program type.  For data files, choose Variable or Fixed, depending on which type of data file you are transferring.

    Hopefully you can now transfer files back and forth with Model II TRSDOS.  Leave a comment to let me know how it works out for you. read more


By | March 4, 2018

I’ve just released my first TRS-80 game called Breakdown. It’s a derivative of the classic video game Breakout with a little bit of Tetris. It’s written in Z-80 assembly and runs on most TRS-80s. The goal of the game is to score as many points as possible by breaking as many bricks as possible with a bouncing ball while trying to keep the ball in play and avoiding falling bricks.  Give it a try and let me know how it goes. read more