I'm hooking up a PS/2 keyboard to try out and I added a couple of 3k3s to +5V and although I know it shouldn't be a problem I thought that nonetheless I should ask the question. I'm not talking about guesses, just any hard facts that we know at this stage. Any other time I would just go for it but at the moment this is my one and only P2. Alternatively I could change the pull-ups to 3.3V but I'm not sure that the keyboard's Vih will comply. Actually, it's easier for me to stick a red LED in series with the +5V to get my 3.3ish volts since I made a little PS/2 socket adapter just to make sure PS/2 works before I try for PS/2 compatibility on USB keyboards.