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Keyboard-less VT10x terminals

jmdhuse

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Hello All,

I've noticed that there any number of VT10x monitors for sale on Ebay, but without the standard VT100 keyboard to go with them, and if you can find a keyboard, they are pretty pricey. I managed to get my hands on a VT101 monitor (no keyboard), and I decided to design a board that would connect to the monitor on one end and a PS/2 keyboard on the other end. The keyboard interface is adapted directly from the DEC schematics for the VT100 keyboard, and uses a microcontroller to receive inputs from the PS/2 keyboard and mimic key switch presses and releases on the VT100 key scan lines. I have it working at this point, and I wondered if there was any interest in such a thing among the community here.

Here is a photo of the current prototype - the final version will have a 1/8" stereo jack so you can use an audio cable (1/4" stereo jack to 1/8" stereo jack) to connect the board to the monitor.
keyface_rev3.jpg
I have tested it quite a bit, and all the functions seem to work correctly. I mapped special keys, like SETUP, PF1 - PF4, etc. to function keys on the PS/2 keyboard - the mapping is done in a table that gets compiled into the firmware, so it can be changed to match your whimsey. I'd be glad to provide the PCB files, parts list, and compiled firmware.

Let me know if you are interested - cheers, Jon.
 

pbirkel@gmail.com

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In case you can't tell by the number of likes, I think that the answer is "yes there is interest" :-}. Nice job!
Will you also make the source code available for local tinkering, please? (Including for recompiling for "whimsey".)

I see an IM6402, but can't read the MCU markings. Which are you using?
 

jmdhuse

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In case you can't tell by the number of likes, I think that the answer is "yes there is interest" :-}. Nice job!
Will you also make the source code available for local tinkering, please? (Including for recompiling for "whimsey".)

I see an IM6402, but can't read the MCU markings. Which are you using?
I'm currently using an STM32F302CB at 64MHz, mostly because I have a bunch of them on hand and they only cost about $7 each. It is overkill for the application, but I am pretty familiar with it and I wasn't trying to minimize the cost.

Regarding the software - all my code is developed using my own libraries of peripheral APIs. I don't use the STMicro HAL layer because I develop for a wide variety of microcontroller architectures and I developed a uniform library of APIs that make it easy to move applications between architectures. I'm reluctant to disseminate it just because of the possibility of people asking for changes and fixes... I don't have the bandwidth and there is not any formal documentation. However, if someone just wanted to mess with the main application and compile with the libraries as they are, I would be open to that.
 

jmdhuse

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Great idea! Could this be expanded to other brands of keyboard-less terminals, such as Wyse? I see a lot of them on eBay minus keyboards too.
I imagine so, and probably a lot simpler, from a circuit perspective. For the VT10x family, DEC used a pretty clever and complicated communication scheme between the monitor and keyboard that mixes clock and bi-directional data all on a single wire. Later keyboard interfaces are simpler, I think. I'll see what I can find out about protocols used with other terminals.
 

F11ACP

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Feb 26, 2023
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Other terminals (VT200-VT400 series) use plain and boring RS232 at 4800 baud (LK201 and LK401/2 series keyboards). The keyboard talks some protocol to the terminal, which then talks to the system. The keyboard codes are here:


See chapter 7, table 7-3, the protocol is described in the following sections...

For VT500 series a standard PS/2 keyboard can be used... DEC's LK411 uses a modification for keycodes and some commands, to accommodate the 108 (aka ANSI) key layout, vs the standard 105-key layout used for PCs...
 

pbirkel@gmail.com

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I'm currently using an STM32F302CB at 64MHz, mostly because I have a bunch of them on hand and they only cost about $7 each. It is overkill for the application, but I am pretty familiar with it and I wasn't trying to minimize the cost.
For those of us with limited SMD/SMT skills, a TSSOP package (0.65mm pitch) would be nicer than a LQFP-48 (0.5mm pitch) :-}. Still I see that the STM32 comes in much worse packages. Agree that $7 isn't going to break the bank on this project.
 

jmdhuse

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Hmmm, I guess I could assemble them myself if there are only a small number, like I did with the MXV/BVD board... with a stencil it doesn't take too much effort...
 

Bitly

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Hmmm, I guess I could assemble them myself if there are only a small number, like I did with the MXV/BVD board... with a stencil it doesn't take too much effort...
Some of the Chinese PCB houses will assemble for a reasonable price. Others here have gone that route with good results.

CW
 

GreyHairedDECfan

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That's great! Other than the LEDs which we messed around with via code, frankly the keyboard from the VT-100 isn't that great. Clunky, terrible key feel, etc. So being able to use a new keyboard with it would be super. Nice job.
 

jmdhuse

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I've ordered the (hopefully) final/production version of the PCB. It will take a couple of weeks to receive it and test it out. I'll keep you all posted on this thread.
 

thevowel

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Jan 24, 2022
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Projects like this are so important - thank you! Looking forward to getting one for myself.
 

BitWiz

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The RP2040 is a dual core 133MHz Coretex M0+, 264K of RAM with 8 separate PIO processors for under a dollar in small quantities.

You could use the 1 PIO processor to handle the Terminal keyboard signaling and one to handle the PS/2 signaling and the CPU to do all sorts of translations and macros on top of normal keyboard functions. A minimum RP2040 system can be built for about $2.00 depending on the side of the QSPI flash chip.
 

jmdhuse

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The RP2040 is a dual core 133MHz Coretex M0+, 264K of RAM with 8 separate PIO processors for under a dollar in small quantities.

You could use the 1 PIO processor to handle the Terminal keyboard signaling and one to handle the PS/2 signaling and the CPU to do all sorts of translations and macros on top of normal keyboard functions. A minimum RP2040 system can be built for about $2.00 depending on the side of the QSPI flash chip.
Yes, I'm sure there are many cheaper solutions... However, due to the clever signaling between keyboard and monitor, it made sense to me to replicate the DEC design and use the 6402 UART, which fixes part of the expense. If this were intended to go into high-volume production, cost would definitely be a factor, but I can't imagine more than a dozen of these things getting built, so not worried about cost. Also, I have already made, over the years, a significant investment in software development, and I am not ready to start that over again with another IO architecture. The SM32F302 SPI module works fine for the PS/2 keyboard interface.
 
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