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Cable Identification Means Using Active Circuitry for Data Communications Signal Cables

IP.com Disclosure Number: IPCOM000036473D
Original Publication Date: 1989-Oct-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Appel, WD: AUTHOR [+4]

Abstract

This article describes a cable identification means which utilizes a single cable pin and a single precision resistor mounted within a cable connector and a precision analog measurement circuit mounted within the device to which the cable is connected.

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Cable Identification Means Using Active Circuitry for Data Communications Signal Cables

This article describes a cable identification means which utilizes a single cable pin and a single precision resistor mounted within a cable connector and a precision analog measurement circuit mounted within the device to which the cable is connected.

In the field of data communications the message format, voltage levels, and terminating impedances of the circuit between the data terminal equipment (DTE) and the data communications equipment (DCE) have been fixed through standardization. This allows data terminals and data communications equipment manufactured by many different manufacturers to be interconnected. There are many different standards, however, and each standard specifies a different number of conductors within the connecting cables. For the DTE to be capable of supporting more than one protocol, there has to be an unambiguous way of establishing whether the proper cable for the desired protocol is installed at system power-up time to prevent inadvertent equipment damage and functional malfunctions.

A common method to establish the cable identity (CID) is to provide means within the cable connector itself to identify the cable type. The DTE connector provides a sufficient number of connector pins that may be either tied down to ground or left floating in a binary pattern. Resistors are provided within the DTE to automatically pull up to a high state the inputs that are left floating. The binary number is then interrogated by the DTE logic to establish the cable type. If the wrong cable is installed, then operation may be inhibited and a message is output to indicate improper configuration. Fig. 1 illustrates this method.

With the capabilities of very large-scale integrated (VLSI) circuits it is possible to allow the DTE logic to support and use a multiplicity of the available interface protocols under software control. Also, it is possible to support multiple cable connections with the same logic due to the relatively slow nature of most data communications data rates compared to the VLSI chip performance capabilities. The good performance allows multiplexing of portions of the logic on chip to support multiple...