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Comment by ndiddy | Hacker News Reader

Keyboards from the late 90s and early 2000s often did something similar. The controller supported both PS/2 and USB and the keyboard would come with a PS/2 plug and a passive adapter. That's why if you're trying to use a PS/2 keyboard designed prior to the introduction of USB (like a Model M) on a modern computer, you need to make sure to get an active PS/2 to USB adapter that actually translates the protocol.

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Yeah, I discovered this the hard way when I tried to plug a somewhat modern keyboard to a pc through ps/2 (for the theoretical interrupt-driven speed) and didn't work.

A lot of mechanical gaming keyboards still support ps/2 though for the aforementioned interrupts.

I guess this has been long solved, but I remember around 2010 or so it was generally still recommended to use keyboards with PS/2 because of lower latency and support for N-key rollover.

I would expect that PS/2 to USB could be handled on the computer.

I have little experience, but from debugging some early 3D printers on Linux, I've learned that the U in USB really stands for universal: that it'll just pass on serial stuff to/from the OS, drivers or software on the computer to handle.

Not really no, the timing requirements of the USB protocol are very tight and handled by dedicated circuits. The exception is microcontrollers where you can sometimes achieve the timing in software.

In addition to electronic singalling being completely different, the serial interface used by many 3d printers is not the same as low level serial interface sent over the wire. There is a low level usb protocol for stuff like data packets ,checksums , metadata negotiation, multiple endpoints in single device, basic transfer types(bulk, isochronous, control, interrupt). All common device types and standard drivers including USB to serial, HID, removable storage is built on top of this layer instead of raw serial sent over the wire. That's why you can have stuff like USB hubs which can forward data to and from multiple devices. And also why you can plug in a USB device, and the OS recognize and lookup driver without user manually configuring what device is plugged into which port.

Having done some embedded development, I am pretty sure that those 3D printers had a serial-over-USB converter like the famous FTDI family of chips. Those chips just simulate a plain old RS232 connection over USB.

There are some motherboards that can switch either PS/2 or RS232 signalling onto USB-A connectors, but this is completely non-standard hack mostly seen on some enterprise stuff few years back that seems to have mostly died away.

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