> If you’re designing a universal port, you will be expected to provide power. This was a lesson learned in the times of LPT and COM ports, where factory-made p

> If you’re designing a universal port, you will be expected to provide power. This was a lesson learned in the times of LPT and COM ports, where factory-made peripherals and DIY boards alike had to pull peculiar tricks to get a few milliamps, often tapping data lines. Do it wrong, and a port will burn up – in the best case, it’ll be your port, in worst case, ports of a number of your customers. I'd never thought about this. Way back then, mice connected via the serial port. It seems like they got their power from the RTS or CTS pin. And that pin isn't 0V/5V, it uses negative and positive voltages, -5V/5V on the low end, more likely -12V/12V according to stuff floating around on the internets. Seems complex. Might research this properly later.