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VT100 to USB Converter Firmware

Version: 1.0 Last Updated: 28 July, 2012

1.0 About

This project contains source code and schematics for a DEC VT100 terminal keyboard to USB converter.

The purpose of the converter is to allow a DEV VT100 terminal keyboard to be used as a USB input device on a modern computer. This is, of course, almost completely useless, but that doesn't mean it's not fun.

2.0 Description

The converter uses a [Teensy 2.0] (http://www.pjrc.com/teensy/) development board powered by an ATmega32U4 microcontroller, which this firmware targets. In addition to the microcontroller, the converter uses an external HD6402 UART, an external clock generator, and a voltage comparator for signalling with the VT100 keyboard.

The firmware is written in AVR C, and can be compiled with the avr-gcc tool chain. The resulting firmware should be loaded onto the Teensy with the Teensy loader.

3.0 Key Mapping

Most keys should be self-explanatory. All alphanumerics and standard punctuation characters map to what you'd expect. Several keys, though, need special attention.

VT100 Key USB Keyboard Key
NO SCROLL Scroll Lock
BREAK Pause / Break
LINE FEED Enter / Return
PF1 F1
PF2 F2
SET-UP Keyboard Config (see 4.0)

The VT100 keyboard is notably deficient in modifier keys compared to a modern USB keyboard, so some sacrifices had to be made. PF3 and PF4 do not map to F3 and F4. Instead, they map as follows

VT100 Key USB Keyboard Key
PF3 Alt (PC) / Option (Mac)
PF4 Windows (PC) / Command (Mac)

4.0 Keyboard Configuration

The VT100 keyboard's built-in speaker can be used to generate key-clicks and an audible bell if the options are set in the USB converter's firmware. The options are persisted in the AVR's non-volatile EEPROM between restarts.

4.1 Bell (SET-UP + B)###

To toggle an audible bell when the ^G (control-G, ASCII BEL) character is sent, hold down SET-UP and press B. The first LED (labelled L1 on the keyboard) will illuminate when the audible bell is enabled.

4.2 Key Clicks (SET-UP + K)###

To toggle key clicks, hold down SET-UP and press K. The second LED (labelled INSERT on the keyboard) will illuminate to show that key clicks are enabled.

5.0 License and Credits

This project is Copyright © 2013 by Seth Morabito, and is distributed under the MIT license. See the file LICENSE.txt for details.

This code makes use of the Teensy USB Keyboard Example Code (usb_keyboard.c and usb_keyboard.h). This code is Copyright © 2009 by PJRC.COM, LLC, and is also distributed by PJRC under the MIT license.

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VT100 Keyboard to USB Converter

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