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The VT100 Terminal

Summer has been filled with distractions, but I’ve finally begun making headway on a DEC VT100 Terminal simulation.

Unlike other VT100 emulators, this isn’t simply an emulation of VT100 protocols. It’s a simulation of the VT100’s 8080 CPU, running the original VT100 Firmware inside the PCx80 CPU emulator, along with other essential components that the CPU interacts with to control the display, keyboard, and serial port.

Most of the VT100’s (non-AVO) functionality should be operational now. Once the VT100 “powers on,” it should clear the screen and briefly display a “WAIT” message as it processes its Non-Volatile RAM (NVR). When you see a blinking cursor, it’s ready to use. Press the SET-UP key to configure the terminal, just as you would an original VT100 terminal.

For even more fun, check out the Dual VT100 Terminals demo.


Function keys are mapped as follows:

From the SET-UP screen, you can press 4 to switch to LOCAL mode and verify local operation of most VT100 keys. The following keys have special meaning inside SET-UP Mode:

The initial goal for the simulation is to provide a virtual terminal that can communicate with other PCjs machines and provide a realistic serial communication experience, all from the comfort of your web browser.

Eventually, I would also like to recreate a fully commented source-code listing for the DEC VT100 ROMs. DEC’s VT100 Technical Manuals are excellent, and they provide an enormous amount of hardware detail, but they are a bit light on certain programming details, and there are no firmware listings like those those that IBM provided in the early IBM PC Technical Reference manuals.

Check out the VT100 Debugger Configuration for additional information about VT100 internals and links to other technical resources.

Jeff Parsons
Aug 3, 2016