Equisys technical notes

Technical guidance, explanations and fixes for our products

PRB: CPI/100-UK does not receive inbound calls when connected to a 2-wire extension socket



ID: ZTN1018

This Zetafax technical note applies to:

  • Zetafax 5.5 and later.
  • Dialogic CPI/100-UK and CPI/100 Light UK boards.


If a Dialogic CPI/100-UK or a DialogicCPI/100 Light UK board is connected to a 2-wire extension socket, it will send faxes correctly but not answer inbound calls.


This problem results from the absence of the wire that provides the ringing indicator. The master socket contains a resistor and a capacitor to provide ringing to the boards. This allows the socket to provide the ringing on the third pin of the master socket. Many phones and other devices, including the CPI/100 and CPI/100 light boards, use this 3rd pin to detect an incoming call, and will not detect incoming calls when this is not present. Some extension sockets are 2 wire extensions and therefore do not give the 3rd pin signal, so these devices can not be used for receiving incoming calls on 2 wire extensions.


A master socket must be used if the CPI/100 or the CPI/100 Light board is expected to receive inbound calls.


This has been confirmed as a problem with these cards.

Last reviewed: 7 October 2005 (GC/EB)

Date Published: 15 May 2000 (GC/GW)

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