I have a Yamaha PSR-550 keyboard. It was released in 2001 (it's as old as me!), and is equipped with MIDI ports:
How can I use the serial MIDI port (marked
to host) with my modern PCs? (They don't have serial ports, and the keyboard appears to be using a non-standard pinout)
A copy of the manual with specifications (hosted on my webserver) can be found here: https://rahul.party/files/psr550-6044.pdf
Also see this short article to learn more about the port.