I'm puzzle about why the diagram on p. 332 in https://www.electro-tech-online.com/custompdfs/2007/11/mikroc_manual.pdf uses all the RS-232 connections other than pin 9. I had only used TXD, RXD, and ground pins in the past with RS-232 cables. After reading https://en.wikipedia.org/wiki/RS-232, I've come under the impression that the rest of the pins are used in a null modem application, but I'm still unsure. Any insights on this?