How does a USB-->PS/2 adapter work?

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kleptophobiac

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How does a USB to PS/2 adapter work? As far as I can tell USB is a vastly more complicated mode of communication than PS/2. Does the mouse or keyboard detect that USB is not functioning properly when they are plugged in and switch over to a different communication protocol? Does anybody know off hand what the pinout for each side of the adapter is?

I have no real need to know, but I just bought a new mouse and the thought hit me as I was plugging it in and chucking the PS/2 adapter.
 
It's not really native to the bus as far as I know, it's more mode switching. The device will recognize that only specific connections are made, and will switch into PS/2 mode. You can't throw a converter onto a modern mouse and expect it to work.
 
The data signals on USB and PS/2 serial are not significantly different. The USB side provides the USB device identification and signal levels and converts to/from PS/2 signals. There's a write-up of this on Wikipedia, IIRC, on one of the USB pages.
 
As far as the mouse goes, the conversion is usually done by a chip in the mouse. The green adapter that comes with new mice is just a mechanical adapter, it doesn't do anything to the signals. The mouse is able to autodetect what kind of port it's attached to.
 
Also, to go the other way (PS/2 devices to a USB port), you can use a chip like the Chesen CSC0101A. It's an ASIC with a 6502 core, RAM, and ROM with a program for doing the conversion.
 
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