You are welcome.

Their documentation can be a bit scattered. On the first RX-Vxxxx RS-232 units one must strap pins 7 and 8 together on the receiver side. Not a Yamaha issue, but some early controllers required some strapping too, usually pins 3 and 4. This was inherited from the early data terminal days when mechanical devices at both ends of the cable would notify each other when they were ready. Now, virtually everything uses a 3-wire connection. In those early days one had to worry about overrunning the partner device on a character by character level. Now we have lots of memory and can buffer large blocks of data, however, in a two-way environment one must be sure that the other side has had enough time to execute a command, or things could get out of sync.

One can also run into some voltage issues because early devices insisted on a +/- voltage range, not the 0-5V range of integrated circuits. Modern RS-232 devices will operate with the 0-5V levels.

As is often the case, Wikipedia is rich with details.