MIDI is similar to RS-232 only if you conflate RS-232 (which specifies voltage levels and physical connector) with asynchronous start-stop serial, while that is

MIDI is similar to RS-232 only if you conflate RS-232 (which specifies voltage levels and physical connector) with asynchronous start-stop serial, while that is the most common application for RS-232, it can be carried over a lot of physical layers and also RS-232 can carry synchronous serial (which is a part of the reason for the DB25 with a lot of “unused” pins). MIDI physical layer is pretty much unique to MIDI and a kind of an ugly, but cheap and reliable (when done correctly), hack. Edit: technically you can wire RS232 transmitter to MIDI receiver and if both follow the respective specification the Tx should not source enough current to blow the Rx optocoupler. But it will generally not work the other way around because in absence of said optocoupler the relationship of the MIDI signal (which is a current loop referenced to more or less unspecified potential) to receiver ground matters.