A few years ago, it was common to find keyboards and mice with PS2 connectors on the cable and a simple passive adapter to allow you to plug into a USB port. I have a couple that went the other way -- USB connector on the cable and an adapter to use PS2, but those were a bit of a rarity. The controller auto-detected which kind of bus it was plugged into based on whether the computer pulled the two data pins high or not.
I'm considering designing something similar, and since most of the higher-powered chips have dedicated hardware to interface with the USB bus, it'd be a shame to not be able to make use of it when it's appropriate.
Since the chips used by teensy all have dedicated pins for the USB, *IN THEORY* I could tie a second pair of pins to the USB port that would float when connected via USB and disable the USB transciever when we needed to use PS2 (or some other kind of bus).
The potentially concerning question that I couldn't find an answer to in the Atmel and Freescale datasheets is: when you disable the USB port, what happens to the data pins? Do they become floating (yay!) or do they get tied to either GND or VUSB? (boo!)
I'm considering designing something similar, and since most of the higher-powered chips have dedicated hardware to interface with the USB bus, it'd be a shame to not be able to make use of it when it's appropriate.
Since the chips used by teensy all have dedicated pins for the USB, *IN THEORY* I could tie a second pair of pins to the USB port that would float when connected via USB and disable the USB transciever when we needed to use PS2 (or some other kind of bus).
The potentially concerning question that I couldn't find an answer to in the Atmel and Freescale datasheets is: when you disable the USB port, what happens to the data pins? Do they become floating (yay!) or do they get tied to either GND or VUSB? (boo!)