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Detection of Cable Opens for Differential Interfaces

IP.com Disclosure Number: IPCOM000103623D
Original Publication Date: 1993-Jan-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 3 page(s) / 91K

Publishing Venue

IBM

Related People

Wojciak, D: AUTHOR

Abstract

A test circuit or wrap block tests a cable leading from a differential driver and a cable leading to a differential receiver. The cable also includes a ground wire.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 54% of the total text.

Detection of Cable Opens for Differential Interfaces

       A test circuit or wrap block tests a cable leading from a
differential driver and a cable leading to a differential receiver.
The cable also includes a ground wire.

      The goal of the circuit is to prevent the output of the
receiver from tracking the output of the driver during either state
of the driver when any conductor within the cable is discontinuous.

      The description below pertains to diagram 1 (proposed
solution).  See Figs. 1 and 2.  Normal operation allows a voltage
swing of approximately 4.0 to 0.4 volts at pins 35 and 36.  When the
voltage at pin 35 is low, the voltage at pin 36 is high and vice
versa.

      The ratio of R1 to R2 is 10 to 1.  This ratio shall be
of a value such that the voltage applied to the receiver input is
less than the threshold value generated by bias resistors R5 and R6.
The voltage shall also exceed the minimum differential voltage
required by the receiver.  If bias resistors are not installed, the
natural bias of the receiver is used.

      When the interface is not used, and no cable is connected,
resistors R5 and R6 bias the receiver inputs at 1.2 and 0.8 volts,
respectively.  This inhibits the receiver from switching when not in
use, generating unwanted noise.

      Should the wire between pins 39 and 12 open, the resistor
combination R1 and R2 causes the voltage at pin 38 to be less than
the threshold value set by R6.

      A...