Path: utzoo!attcan!uunet!zephyr.ens.tek.com!uw-beaver!milton!dali.cs.montana.edu!rpi!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ucselx!bionet!hayes.ims.alaska.edu!accuvax.nwu.edu!nucsrl!telecom-request From: john@bovine.ati.com (John Higdon) Newsgroups: comp.dcom.telecom Subject: Re: A/A1 Control For Key Telephone Systems Message-ID: <14019@accuvax.nwu.edu> Date: 25 Oct 90 19:42:00 GMT Sender: news@accuvax.nwu.edu Reply-To: John Higdon Organization: Green Hills and Cows Lines: 38 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 762, Message 12 of 13 "Dennis G. Rears (FSAC)" writes: > Can anybody tell me what is meant by A/A1 control for key telephone > systems? Also what is a 1A2 key system? A reference would aalso be > good. A 1A2 key system is the formerly ubiquitous arrangement found in small businesses. Typically the phones had a thick cable and six buttons across the front that represented outside lines and would light when the line was in use. For larger operations, there were ten, twenty, even thirty-line phones. Various types of intercoms were available. Actually, these systems are still available new if you don't mind basics. The A/A1 leads for each line controlled what the KSU (central unit) did with the line. The A lead is the actual control lead and the A1 is ground. When you come off-hook on a line, the A/A1 pair is closed through the switchhook. This causes the light to come on. When you hang up, the pair opens and the light goes out. Now for the magic. If you open the pair without opening the Tip/Ring pair (as the HOLD button does) then the KSU will sieze the line and wink the light. You may then open the Tip/Ring pair (button pops up) without losing the call. Reclosing the A/A1 pair and the Tip/Ring pair (pushing the button back down) re-accesses the line. If the line is ringing (light flashing), then closure of the A/A1 pair signals an answer. As far as a reference goes, I learned what I know about 1A2 from Direct Experience (tm). Data sheets that come with KSUs pretty much assume you know all about it (or don't care), since they only tell you where the wires go. Back when I learned 1A2, this was all handled by the telephone company and ordinary people had "no legitimate need" for such information, hence there weren't many references. It is probably a different story now. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@bovine.ati.com | San Jose, CA 95150 | M o o !