107 lines
3.5 KiB
Markdown
107 lines
3.5 KiB
Markdown
# Keyboard Converter: Consul 262.5 & VDX 52600
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Arduino project for a keyboard converter between a Zbrojovka Consul 262.5 terminal keyboard and a Videoton VDX 52600 terminal.
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Why? Because the VDX 52600 terminal doesn't use the AT or XT keyboard protocol. And neither does the Consul 262.5.
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This converter aims to translate between the two non-standard protocols, making these devices usable!
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## Keyboard: Consul 262.5
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Terminal keyboard from 1980s built in Brno, Czechoslovakia.
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It uses a DB25 connector with UART TTL data lines, clock line, +5V primary power and -12V auxiliary power.
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The -12V voltage alone makes in unusable with the current computer hardware, so a converter is necessary.
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## Terminal: VDX 52600
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VT52 terminal from 1987 built in Hungaria.
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The serial interface is an RS-232 on a DB25 connector.
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It features a DIN5 keyboard connector that does not use the standard AT/XT keyboard protocol.
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## Converter
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Interfaces the keyboard and the terminal, optionally a USB. These modes of operation are supported:
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1. Keyboard and terminal connected: primary standalone mode. Everything is powered from the terminal.
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2. Keyboard and USB connected: USB keyboard mode. Powered from the USB which acts as a HID keyboard.
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3. Terminal and USB connected: Serial keyboard over USB mode. Powered independently. Allows sending keystrokes to the terminal over USB serial.
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## Parts needed
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- Arduino Leonardo
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- Symmetrical boost converter, 5V to +/- 12V
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- Piezo speaker
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- red and green LED + 470 ohm resistors
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- connectors
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- project box
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- (among others)
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## Connections
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### Terminal DIN5
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Device | Controller | Description
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---|---|---
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GND | GND | Ground
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+5V | +5V | Power
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Data | 6 | Keyboard data to terminal
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Status | 7 | Status (LEDs) and Clock from terminal
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### Keyboard DB25
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Device | Controller | Description
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---|---|---
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GND | GND | Ground
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+5V | +5V | Power
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-12V | -12V | via a symmetrical boost converter
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Serial out | 3 | UART out from keyboard
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Serial in | 4 | UART in to keyboard
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### Box Interface
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| Controller | Description |
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| ---|--- |
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| 10 | Offline LED |
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| 9 | Online LED |
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| 8 | Speaker |
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## VDX 52600 keyboard protocol
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Since I didn't have any compatible keyboard, I tried reverse-engineering the protocol. Following are my findings:
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- on the Status pin, the terminal periodically sends out a status "packet" with the state of LEDs
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- on the Data pin, the keyboard sends 8-bit key codes
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- it seems to rely on a shared baud rate, expecting the keyboard to synchronize on the periodic status messages sent by the terminal
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- the terminal is not listening for key codes while it is transmitting the status packet
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## Terminal's DB25 connector
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The VDX 52600 terminal uses the standard RS-232 serial link through a DB25 connector. It is enough to connect pins (2) TX, (3) RX and (7) GND.
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See [RS-232 over DB25 connector](http://www.nullmodem.com/DB-25.htm) for more.
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Beware that this is an RS-232, so the voltages are not safe for a standard USB-to-serial module. Use an RS232-to-TTL converter such as the MAX232 chip.
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By default the serial port configuration is 9600–8-N-1 (i.e. the standard baud rate of 9600).
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Connecting it to a serial port of a Linux machine works nicely and you get a vintage console experience.
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## Links
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- [Videoton VT terminal family (in Hungarian)](https://itf.njszt.hu/termek_hardware/vt-videoterminal-csaladok)
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- [Consul 262.5 technical details and manual (in Czech)](http://www.sapi.cz/prislusenstvi/c262-5.php)
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