Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Reexamination Certificate
1998-07-14
2001-02-20
Follansbee, John A. (Department: 2154)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
Reexamination Certificate
active
06192433
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to computing systems with bus-connected peripheral devices, and more particularly to systems using small computer system interface (SCSI) bus structures.
An important and valuable part of any computing system today is its external storage facility. The presently preferred form of external storage is some type of hard disk structure because of its random access capability although other forms (e.g., tape, CD-ROM) are also used. This type of external storage is often used as (or called) mass storage. Mass storage which, as the name implies, is used to retain for later access huge amounts of data. When later accessed it is advantageous that the access be made as quickly as possible. While there are a number of bus architectures capable of connecting a processor unit to such mass storage devices, one that is very flexible and powerful, particularly for connecting hard disk mass storage devices, is the small systems computer interface (SCSI).
The physical SCSI bus structure comprises a set of conductive signal lines that carry data and control signals for information transfer between the devices on the bus. Signals and data are communicated according to pre-determined protocols. (See, for example, Working Document for Information Technology SCSI Parallel Interconnect 2 (SPI-2), ANSI X3.302.)
One well-known physical characteristic of SCSI bus structures is that the signal lines forming the bus are terminated by an SCSI bus terminator at each end of the bus. If there are multiple devices connected to the bus and the SCSI terminators are built into the last device at each end of the bus, then problems can occur when the last SCSI device on the bus must be removed or shut down. Removal/disconnection of the last device with the terminator degrades the signals communicated on the SCSI bus so that the entire system is brought down. In order to continue operation, the SCSI termination must be moved to the next in line last device on the bus.
This problem can also occur if the connection of the last device is inadvertently disconnected, the entire system will again be affected because the communicating ability of the SCSI bus is lost.
SUMMARY OF THE INVENTION
The present invention provides a method, and apparatus for implementing that method, that allows for on-line service of a failed element located at the end of a SCSI bus which included the SCSI cable terminator.
The invention is described in the context of a computing system in which processor units are coupled to peripheral devices (e.g., storage units) by a SCSI bus architecture. According to the present invention, there is provided each device immediately next to the system element that forms the last in line on the bus (i.e., the one with the SCSI cable terminator) a termination adapter circuit. In the event the last device is removed or looses power, the termination adapter circuit will sense that removal or loss of power and automatically disconnect the SCSI bus connection to the former last device and connect a new SCSI terminator. This immediate proximate device then forms the last device on the SCSI bus, providing the requisite SCSI bus termination.
Conventionally, a SCSI bus structure includes, among the signal lines implementing that structure, the signal “Termination Power” (TERM PWR), a 5 volt signal that supplies current to the terminators at the end of the SCSI bus. In a preferred embodiment of the invention, TERM PWR is monitored by a termination adapter circuit located in association with that device next in line on the SCSI bus to the device lost on the SCSI bus, i.e., the one with the built in SCSI bus terminator. Should that last device loose power, or the connection to the last SCSI device is interrupted, the TERM PWR signal will be lost. The loss of TERM PWR will be noted by the termination adaptor circuit, causing it to switch in a new SCSI bus terminator and electronically disconnect the bus to the former last device. Thereby, the SCSI bus for data transfers remains.
The implementation is symmetric; the termination adaptor is located in each of those devices immediately proximate the next in line from the last devices on the SCSI bus. Therefore, the loss of a device on either end of the SCSI bus follows a similar procedure.
A number of advantages are achieved by the present invention. First, an end device such as a CPU can be removed from the SCSI bus, or shut down for repair, without having to shut down the entire system connected to the SCSI bus even temporarily. Thus the remaining CPU can continue to operate.
Further, should the SCSI bus cable that connects to the last device on the bus be disconnected, the entire system is not caused to fail.
This invention is particularly useful in non-stop computer systems that require repair while the rest of the system continues to operate.
REFERENCES:
patent: 5467453 (1995-11-01), Kocis
patent: 5564024 (1996-10-01), Pemberton
patent: 5586271 (1996-12-01), Parrett
patent: 5596757 (1997-01-01), Smith
patent: 5613074 (1997-03-01), Galloway
patent: 5628637 (1997-05-01), Pecone et al.
patent: 5680555 (1997-10-01), Bodo et al.
patent: 5748910 (1998-05-01), Herrera E.
patent: 5751977 (1998-05-01), Alexander
patent: 5758101 (1998-05-01), Pemberton
patent: 5919253 (1999-07-01), Schneider
patent: 5920266 (1999-07-01), Allgood et al.
patent: 5983296 (1999-11-01), Lamkin et al.
patent: 6029216 (2000-02-01), Hoglund et al.
patent: 6047379 (2000-04-01), Larabell et al.
patent: 6055582 (2000-04-01), Pascarella et al.
patent: 6061754 (2000-05-01), Cepulis et al.
Chan Wing
Griffith David L.
Follansbee John A.
Tandem Computers Incorporated
Townsend and Townsend / and Crew LLP
LandOfFree
Automatic SCSI termination readjustment does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Automatic SCSI termination readjustment, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Automatic SCSI termination readjustment will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2575151