dejvino/consul-vdx-term-keyboard-converter
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Add more info about the terminal and the keyboard

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Arduino project for a keyboard converter between a Zbrojovka Consul 262.5 terminal keyboard and a Videoton VDX 52600 terminal.
Why? Because the VDX 52600 terminal doesn't use the AT or XT keyboard protocol. And neither does the Consul 262.5.
This converter aims to translate between the two non-standard protocols, making these devices usable!
## Keyboard: Consul 262.5
Terminal keyboard from 1980s.
Terminal keyboard from 1980s built in Brno, Czechoslovakia.
It uses a DB25 connector with UART TTL data lines, clock line, +5V primary power and -12V auxiliary power.
The -12V voltage alone makes in unusable with the current computer hardware, so a converter is necessary.
## Terminal: VDX 52600
VT52 termnial with a DIN5 keyboard connector that dones not use the standard AT keyboard protocol.
VT52 terminal from 1987 built in Hungaria.
The serial interface is an RS-232 on a DB25 connector.
It features a DIN5 keyboard connector that does not use the standard AT/XT keyboard protocol.
## Converter
@ -71,10 +78,29 @@ Serial in | 4 | UART in to keyboard
| 8 | Speaker |
### Terminal DB25
## VDX 52600 keyboard protocol
The VDX 52600 terminal uses the standard DB25 serial connector to connect to an RS-232 serial link. It is enough to connect pins (2) TX, (3) RX and (7) GND.
Since I didn't have any compatible keyboard, I tried reverse-engineering the protocol. Following are my findings:
- on the Status pin, the terminal periodically sends out a status "packet" with the state of LEDs
- on the Data pin, the keyboard sends 8-bit key codes
- it seems to rely on a shared baud rate, expecting the keyboard to synchronize on the periodic status messages sent by the terminal
- the terminal is not listening for key codes while it is transmitting the status packet
## Terminal's DB25 connector
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.
See [RS-232 over DB25 connector](http://www.nullmodem.com/DB-25.htm) for more.
By default the serial port configuration is 9600–8-N-1 (i.e. the standard baud rate of 9600). Connecting it to a serial port of a Linux machine works nicely.
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.
By default the serial port configuration is 9600–8-N-1 (i.e. the standard baud rate of 9600).
Connecting it to a serial port of a Linux machine works nicely and you get a vintage console experience.
## Links
- [Videoton VT terminal family (in Hungarian)](https://itf.njszt.hu/termek_hardware/vt-videoterminal-csaladok)
- [Consul 262.5 technical details and manual (in Czech)](http://www.sapi.cz/prislusenstvi/c262-5.php)