Path: utzoo!attcan!uunet!lll-winken!netsys!vector!nobody From: brian@umbc3.UMD.EDU (Brian Cuthie) Newsgroups: comp.dcom.telecom Subject: Re: jack wiring info wanted Message-ID: Date: 12 Oct 88 04:18:44 GMT Sender: chip@vector.UUCP Lines: 31 Approved: telecom-request@vector.uucp (USENET Telecom Moderator) X-TELECOM-Digest: volume 8, issue 160, message 1 X-Submissions-To: telecom@bu-cs.bu.edu (TELECOM Digest Coordinator) X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) In article smb@research.att.com writes: >X-Administrivia-To: telecom-request@vector.uucp (USENET Telecom Moderator) > >I'm interested in the wiring of the 50-pin jack for for 5-line keyset >telephones (2565HKM, if it matters). So far, I've learned that >there are 3 pairs allocated to each line, with 1 pair being tip and >ring, and the third pair being A and A1. I'm especially interested >in pins that are activated by the hold button, especially per-line >hold signals. > > --Steve Bellovin > smb@ulysses.att.com > {att,ucbvax}!ulysses!smb Actually, in a 1A2 key system (that's what those five button phones are used for) the hold button works a little differently. When a phone is off hook, the KSU module detects loop current and the A1 lead activated by the button. So long as A1 is present with the loop current the line is considered to be active. However, if there is loop current but no A1 the line is placed on hold until A1 is present again or the loop current is dropped by the CO (usually indicating the the distant caller hung up). Thus, the hold button actually interrupts the A1 lead just prior to releasing the line key on the phone. This presents the condition described above and thus places the call on hold. This is also why answering machines and modems without A1 leads will leave a 1A2 system line on hold. Terminating a call normally requires that loop current be dropped along with A1. Cheers, brian