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Differential-Single-Ended SCSI Interface Description

IP.com Disclosure Number: IPCOM000120366D
Original Publication Date: 1991-Apr-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 5 page(s) / 201K

Publishing Venue

IBM

Related People

Dimmick, RF: AUTHOR [+3]

Abstract

In order to perform concurrent maintenance on the single-ended SCSI- connected devices, it is necessary to isolate a suspected device from the other devices which may also be active on that bus. The disclosed accomplishes isolation of the device by providing a multiplex switch which investigates the activity on the SCSI-connected devices during the bus-free, arbitration, and select states. (Refer to Figs. 1a, 1b and 1c.) The bus-free state is detected only as the necessary precondition to getting to the arbitration state. In the arbitration state, the differential-single-ended (D-SE) card determines the winner of the arbitration activity and insures that the winner of the arbitration state is connected as one of the communicating pair.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 42% of the total text.

Differential-Single-Ended SCSI Interface Description

      In order to perform concurrent maintenance on the
single-ended SCSI- connected devices, it is necessary to isolate a
suspected device from the other devices which may also be active on
that bus.  The disclosed accomplishes isolation of the device by
providing a multiplex switch which investigates the activity on the
SCSI-connected devices during the bus-free, arbitration, and select
states. (Refer to Figs. 1a, 1b and 1c.)  The bus-free state is
detected only as the necessary precondition to getting to the
arbitration state.  In the arbitration state, the
differential-single-ended (D-SE) card determines the winner of the
arbitration activity and insures that the winner of the arbitration
state is connected as one of the communicating pair.  In the select
state, the D-SE card monitors the arbitration state winner, and
connects the selected address to the arbitration winner. For all
future activity on the SCSI bus, the connected pair perform as a
point-to- point connection.  The select and busy signal lines are
repeated to all nonparticipating nodes within the SCSI network.  The
current design point provides a one-to-two multiplex function.  The
initial design point required a one-to-four multiplex function and
the implementation allows for this extension.  It is also possible to
extend the design point to include a one-to-eight design point if the
requirement ever exists.

      As mentioned earlier, the three RAS functions, which were added
to the standard SCSI architecture definition, are a wrap capability
for the differential SCSI side of the bus, a bus degate function and
a selective reset for the single-ended SCSI side of the
implementation.  The wrap capability allows the initiator to command
the D-SE card to take a specific set of signals received from the
initiator and send that set of signals back to the initiator on a
different set of lines.  The net result of the wrap activity is that
the initiator can test the cable connecting the initiator to the D-SE
card, the drivers/receivers on the initiator, and the
drivers/receivers on the D-SE card. Although this does not isolate a
fault to one of these specific functions, it does isolate the
differential portion of the implementation from the single ended
portion of the implementation.  The bus degate function allows for
deactivation of the bus receivers on the D-SE card to electrically
isolate a selected bus.  This capability allows stuck faults in the
devices, or on the device buses to be isolated.  Once a bus with a
stuck fault has been degated, normal operations can continue on the
undegated bus.  The selective reset capability is an extension on the
reset capability provided on the multidrop definition of the SCSI
bus.  This extension allows for a specific device to be reset as
opposed to the architected definition of reset, which when active,
causes all drops on the SCSI bus to be reset in parallel.  T...