Keyboard Ghosting | Hacker News Reader

Keyboard Ghosting

microsoft.com

27 pointsdenzil_correa16 comments

Most mechanical keyboards have N-Key Rollover or Anti-Ghosting to handle the situation of multiple simultaneous key-presses. USB supports up to ten keys, while only PS/2 has full N-Key Rollover support.

Here's a good explanation of the issue with an interactive typing test showing the issue: http://blog.controlspace.org/2010/08/n-key-rollover-what-it-...

USB keyboards can get around the ten key limitation by presenting themselves as multiple devices.

Or by using a passive USB to PS/2 adapter. USB and PS/2 are both serial protocols with similar wiring, so a USB keyboard that supports passive adapters can detect what kind of port it is plugged into when powered on, then send unmodified PS/2 through the USB cable. For this reason, there are a few mechanical keyboards that only support N-key rollover in PS/2 mode, dropping down to 10-key rollover in USB-HID mode (it's cheaper and less likely to cause bugs than presenting as multiple HIDs, and anyone that cares about N-key rollover probably has a PS/2 port anyway).

I never got why keyboards don't just use a demux / output selector.

Tie each switch through a diode, toggle one column to high, read the rows. Repeat, scanning through all columns.

But then again, it's kind of pointless, what with USB limitations (!) and all.

Because of historical expectations about the semantics of the "Escape" key, IIRC.

Elaborate?

FYI, this was posted a couple times before and once with some discussion associated.

https://news.ycombinator.com/item?id=7358333

They never actually say what they do.

To counter ghosting over USB? They use a different protocol than the HID keyboard protocol. If you're not constrained by that protocol, you can send as many key combinations as your keyboard is capable of generating.

Of course, this means that you need custom keyboard drivers, either installed via a package or by default, and the keyboard needs to be capable of switching protocols, based on if its talking to a OS with compatible drivers or a BIOS without.

Anyone knows about such keyboard but in smaller size, as in whatever those left column keys are? Also this looks like an "amazing artwork" I just want a damn keyboard that is small, works and looks boring.

Take a look at either the Vortex Poker (POK3R as the current iteration) or the Atomic/Planck.

Thx a lot Zuikaku! Hahaha, that's minimal :) Will check it out more later.

I totally fall in love with Pok3r, thx again for the reference!

Funnily the main reason I was interested in that anti-ghosting was that I have a keyboard rewriting script that maps the CAPS to be a function key, I'm using IJKL as arrows for example. And now I have to realize I'm not the first person who thought about that. Pok3r ships with that by default.. Really?! I feel like in wonderland... :D

Hmm, on rMBP the S-D-C combo does not work, who would have thunk it, never wondered about this. Educational :)

Since the Microsoft Mouse I've always thought MS a better hardware company than software one.

How odd I have a MS mouse and I thought, hmm, if their mouse is so good I'm going to try their keyboard.

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