Not sure what you mean by programming an additional extention. All you have to do is plug it in - in the next available slot - and it will work. To get into programming you need a 20L Operator phone or WinSPM software plus connectors between a PC and your Legend processor Admin port. At the 20L, to get into programming - press menu, system program, and exit or start (depending on software version). Press "Home" to leave programming.
Tom Daugirdas,
President
STCG, Inc.
stcg.com