https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_PS/2_and_USB https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_P... PS/2 is a flavor of lin

https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_PS/2_and_USB https://en.wikipedia.org/wiki/PS/2_port#Conversion_between_P... PS/2 is a flavor of line serial communication (0 and 5V): ground, power, clock, data. "PS/2 mice send interrupts at a default rate of 100 Hz when they have data to send to the computer." Which is how a 'dual mode controller' would drive it's IO pins in a way that work for USB or PS/2. USB uses https://en.wikipedia.org/wiki/Differential_signalling https://en.wikipedia.org/wiki/Differential_signalling , which Wikipedia's article explains have the advantages of greater signal to noise ratio and resistance to some common types of data-channel noise. I don't happen to know what the _data_ voltage level of a USB link is offhand and skimming the article was insufficiently clear (Either of -5V and +5V, OR float is ~2.5V and one pulls up to Vcc the other down to Gnd make some sense.). The initial power pin level is also supposed to be ~5V. -- Also, if you mean from a typical PC... A modern AMD system's block diagram shows most USB ports driven from CPU socket pins or from the primary board chipset directly (E.G. AMD's X870E or whatever). I would be almost amazed if those weren't in house / licensed ASIC blocks with ROM firmware.