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Tandy Hi-Res Joystick Adapter

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Looking for CoCo help? If you are trying to do something with your old Color Computer, read this quick reference. Want to contribute to this wiki? Be sure to read this first. This CoCo wiki project was started on October 29, 2004. --OS-9 Al

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Home / Hardware - Tandy Hi-Res Joystick Adapter

Tandy High-Resolution interface

Name Tandy High-Resolution interface
Interface Joystick Port
About the Hardware Info Box

Aaron gault The High Resolution Joystick

The normal joystick for the Coco is a simple potentiometer. That means it is a variable resistor with one end at 5v DC, the other at ground, and measurements taken from a variable tap. The measurements are made with the Coco ADC/DAC but this device is a 6 bit unit and can only resolve 64 distinct values.

Unfortunately, this method does not have sufficient resolution to handle even the PMODE graphics screens much less the Coco3 HSCREEN modes. Therefore Tandy and several other companies created a high resolution joystick adapter. These adapters use timed RC (resistance/capacitance) circuits instead of a potentiometer. The two most popular were the Tandy and CocoMax units. The circuits were slightly different but it was possible to adapt the Tandy unit by adding a switch so that either type could be selected at will; see diagram.

There was virtually no software written other than the RAT, CocoMaxIII, and Max10 which used the highres adapter under Basic. OS-9 had built-in support for the adapter, but again the Coco community did not write programs requiring the unit.

I present here a simple Basic program to demonstrate how the adapter can be used in either the Tandy or CocoMax modes. Most of the work is done by an assembly language routine, one for each mode. This is not the only way to write useful code, it is just an example to get you started on your own projects. Keep in mind that the timed circuit values change when the Coco CPU clock changes. It may be difficult to get the full resolution at fast clock speeds. demo Basic program and 2 asm source code files in EDTASM format binary files included plus Tandy/CocoMax circuit (joystick.gif)



High-Resolution Joystick Interface Owner's Manual

    • Special Software is Required

The High-Resolution Joystick Interface is specially designed for use with the Tandy Color Computer 2 or Tandy Color Computer 3. Used with the Deluxe Joystick or Color Mouse, the Interface provides a highly accurate method of cursor control that can access up to 640 x 192 pixel resolution. It utilizes the cassette output of the Color Computer to convert analog voltage levels of the joystick into pulses of varying duty cycles.

This conversion requires special software which will provide the necessary pulses into the Interface. Ask for information on available software which supports the High-Resolution Joystick Interface at your Radio Shack Computer Center or store.


The Interface is a very precise electrical device. Handle it with care. Do not drop, hit, or subject it to shock.

  • Do not attempt to pull out the connectors by the cables. It may cause damage to the cable and the connectors.
  • Do not carry the interface by the cable.
  • Do not use the Interface in extreme temperatures (either high or low) or in direct sunlight.
  • Do not spill liquid on the Interface.
  • Do not disassemble the Interface.
  • Should your Interface fail to operate properly, take it to your local Radio Shack Computer Center or store.


Resolution: 640 x 192

Operating Temp. Range: 55 to 85ºF (12.8 to 29.4ºC)

Storage Temp. Range: -40 to 180ºF (-40 to 71ºC)

Humidity: 40% to 80% RH (non-condensing)


Before connecting the Interface, be sure that power to the Color Computer and peripherals is turned off.

1. Connect the 6pm DIN connector 1 of the Interface to one of the 2 JOYSTICK lacks of the Color Computer.

2. Connect the 5 pin DIN connector 2 of the interface to the CASS jack of the Color Computer.

3. Connect the 8-pin DIN connector of the Deluxe Joystick to the jack 3 on the Interface.


Your joystick or color mouse will operate just as if were connected directly to the Color Computer. Note, however, that the resolution on the display will be 10 times higher than normal.

To begin using the Color Computer with the Interface, load the appropriate program and RUN it.