For RS485, RS422, RS232 and RS423.

Documentation with download.

Protocols and computer networks, by Dr. D. Koren of Tel-Aviv University.

RS-232 was created for one purpose, to interface between data terminal equipment and data communications equipment employing serial binary data interchange.

Describes interfacing the Serial (RS-232) Port in relation to both Hardware and Software. Gives Practical Examples using CDP6402 UART and Software Examples in C.

Tutorial discussion of the RS232 (EIA232) standard with signal names, definitions, and examples.

RS232 - overview of RS-232 standard - HW serever, serial, interface,

RS-232 Serial Communications is not that hard.