A Microsoft developer explains how an adapter that converts USB connectors that were once attached to mice and keyboards into PS/2 connectors works



In recent years, many PC peripherals have adopted USB or Bluetooth to connect to PCs, but until USB became mainstream in the mid-2000s, connections via

PS/2 connectors were common. Raymond Chen, a developer at Microsoft, explains how an adapter that converts a USB Type-A terminal, which was once included with some mice and keyboards, into a PS/2 connector works.

A note on the USB-to-PS/2 mouse adapter that came with Microsoft mouse devices - The Old New Thing
https://devblogs.microsoft.com/oldnewthing/20250325-00/?p=110993



Basically, USB and PS/2 are completely different protocols and are not compatible. Therefore, adapters that convert USB Type-A terminals to PS/2 connectors only support a physical connection called 'mechanical (passive)' and do not convert the protocol.

Still, when asked why USB devices connected to a PS/2 connector using an adapter still work, Chen explained, 'These devices have a mechanism that detects whether they are receiving signals from a USB port or a PS/2 connector and changes their behavior accordingly.' In other words, the device itself selects the appropriate connection type from USB or PS/2 when it is powered on.

Chen likens this mechanism to

a power adapter , saying, 'The power adapter itself has no intelligence; it just converts one power plug into a plug shape that can be used in another country. The real power lies in the device it's powering or its power supply.'

According to a user on the bulletin board site StackExchange, around 2014, most devices were capable of receiving both 'signals from the USB port' and 'signals from the PS/2 connector', but since around 2019, the number of devices that can only receive signals from the USB port has been increasing , and in recent years, devices that support PS/2 have been gradually phased out.



Therefore, Mr. Cheng warns, 'Even if you find an adapter that converts a USB Type-A terminal to a PS/2 connector, do not connect it to a PS/2 connector. This adapter is just a physical adapter, and the actual protocol conversion is performed by the mouse itself, which can change its behavior according to the USB and PS/2 signals. '

In recent years, many active converters have been developed to allow devices that do not support PS/2 connectors to be used with older PCs. Developer dekuNukem has released the open source active converter 'USB4VC' that allows wireless mice and wireless controllers to be used with older PCs.

GitHub - dekuNukem/USB4VC: USB Keyboard/Mouse/Gamepads on Retro Computers!

https://github.com/dekuNukem/USB4VC



In addition, engineer Andy Rastelli has released 'HIDman' on GitHub, an active converter that supports almost all USB keyboards and mice.

'HIDman' that allows you to use USB-connected mice and keyboards even on old PCs that do not have USB ports - GIGAZINE

Related Posts:

in Hardware, Posted by log1r_ut