Browse Prior Art Database

Universal Wrap Tool for Small Computer System Interface

IP.com Disclosure Number: IPCOM000116750D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 123K

Publishing Venue

IBM

Related People

John, GD: AUTHOR [+2]

Abstract

A univeral wrap tool for Small Computer System Interfaces is disclosed. The tool allows loopback of SCSI signals in such a manner that the continuity and correct operation of the interface can be determined without interconection to a host, aiding in problem isolation and machine diagnostics. This tool has the following special features: o Operates for both Single Ended (SE) SCSI and Differential (DE) SCSI on a Target or Initiator. o Provides a means for microcode to detect it is present. o Operates with or without TERMPOWER sourced by the device.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Universal Wrap Tool for Small Computer System Interface

      A univeral wrap tool for Small Computer System Interfaces is
disclosed.  The tool allows loopback of SCSI signals in such a manner
that the continuity and correct operation of the interface can be
determined without interconection to a host, aiding in problem
isolation and machine diagnostics.  This tool has the following
special features:
  o  Operates for both Single Ended (SE) SCSI and Differential (DE)
      SCSI on a Target or Initiator.
  o  Provides a means for microcode to detect it is present.
  o  Operates with or without TERMPOWER sourced by the device.

A common wrap tool operates with Differential (DE) or Single Ended
(SE) SCSI devices, even though the connector pin-out and electrical
drivers are different for the two types of interfaces.  This is
accomplished as follows:
  o  A specific wrap scheme of signals is used such that no grounds,
      termpower, or reserved lines are wrapped to active signals for
      either case and so each active signal is observable in both
      cases.  This wrap scheme is depicted is Fig. 1.  Note some
      signals are triple-wrapped, i.e., three signals dotted on the
      same net.  Microcode asserts one of the signals at a time and
      monitors the resultant output.  In this manner, all active
      signals for both SE and DE may be tested.  Note that other wrap
      schemes based on the same concept are possible.
  o  A specific microcode scheme is used to control and monitor the
      signals as pictured in Fig. 2.  If microcode has knowledge of
the
      card type (DE or SE), it branches accordingly and runs the
      appropriate test.  Alternatively, microcode may run both SE and
      DE tests and verify that one passed and the other failed.  This
      will not damage the device and has the advantage that the card
      type is self-determining.
  o  Large-valued pullup and pulldown resistors are present (Fig. 1,
      R1) in the wrap plug to make the plug electrically compatible
      with SE (open collector) or DE (differential push-pull) drivers
      and receivers.
  o  A "light" termpower source network is provided by the SCSI
device
      to source the small amount of power required by pullup/down
      networks to operate properly. ...