"serial-port" seems like, when used correctly, it would indicate the serial port itself, making it a hardware question not belonging on AskUbuntu. Wouldn't the correct tag be "serial-bus" or something? Ditching it for just "serial", as neon_overload suggests, would be a step in the right direction.
serial-port tag should be used when you have questions about ports. Serial ports means that the data "streams" after each other and not at the same time as it is possible right now with parallel cables. So for example universal serial bus or short USB is a serial port.
while the tag serial can also be used if you have questions about serials in terms of keys or to do something in serial.
Sorry for my english, but I guess there is a difference between this tags.