http://www.485solutions.com/rs232.asp

RS232 = Voltage driven
RS485 = Current driven.

Thus the need for a converter. Lap top com ports are configured for RS232. (Maximum cable length = 25' due to voltage drop"
RS485 = 1000' max cable length due to current driven..

Plenty to pick from on the net as you point out.

It Don't mean a thing if it aint got that swing.

Cool, Free, Johnny Smith courtesy of NPR..HERE
http://www.npr.org/ramfiles/asc/asc25.smith.asx