It's your friendly electronic hobbyist again.
I am designing a board where I am reading input from an optoisolator like this.
IN7 is connected to a peripheral parallel port chip of an old 8-bit microprocessor, which is supposed to be set as an input.
I just realized, however, that a user could accidentally have IN7 set as a 5V TTL output instead of an input.
What happens in a case like this? Could doing so cause damage to the circuit? If so, is there a way to protect it?
I'm afraid I don't understand optoisolators (or transistors) well enough to know what would happen.