From 2c1cee18052e44016a31838061787d58d16a1f8c Mon Sep 17 00:00:00 2001 From: Dejvino Date: Sun, 5 Jan 2025 10:11:09 +0100 Subject: [PATCH] Add more info about the terminal and the keyboard --- README.md | 36 +++++++++++++++++++++++++++++++----- 1 file changed, 31 insertions(+), 5 deletions(-) diff --git a/README.md b/README.md index cf8bb2d..58c51ea 100644 --- a/README.md +++ b/README.md @@ -4,15 +4,22 @@ 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)