Digital Equipment Corporation

Compaq Computer Corporation, Inc.

Fee Lee

William Edward Ham

Keith Childs

Charles Monia

A SCSI bus expander provides signal conditioning for transmitted data pulses that is particular to a negotiated data transfer rate. The expander monitors the bus arbitration to determine the devices involved in the transfer, and thereafter monitors the data transfer rate negotiations to determine the transfer rate to be used by that particular combination of devices. An indication of the transfer rate is stored in a memory device at an address determined by the device IDs. The transfer rate is then used to select tap values for tap lines that modify the pulse width and/or a propagation delay of the pulse, so as to correct for signal degradation and to align it better relative to other signals during data transmission. The specific tap values may vary for the different combinations of transmitting and receiving devices involved in the transfer, since the manner in which the pulse characteristics should be modified may be different for different transmission rates.

Method and apparatus for dynamic signal modification on a parallel bus

A SCSI bus extender apparatus coupling a main SCSI bus to a auxiliary SCSI bus includes a mechanism for detecting and processing SELECTION and RESELECTION signals transmitted between the two buses to accommodate target devices on the auxiliary bus which support tagged queuing in accordance with the SCSI protocol. The invention contemplates reserving an address on the auxiliary bus for each initiator on the main bus and performing the appropriate address conversions to enable target devices to properly identify the correct initiator device during a RESELECTION phase.

SCSI bus extender utilizing tagged queuing in a multi-initiator environment

A delay circuit comprises a tapped delay element line constructed from delay elements with fixed delay intervals and a multiplexer for selecting the signal at one of the taps to produce a variable delay through the circuit. The multiplexer is controlled by a selection circuit which receives an input indicative of the actual delay time through the delay circuit from an oscillator constructed from the same fixed delay elements as the delay line.

Auto-calibrating digital delay circuit

A SCSI bus extender apparatus coupling a primary SCSI bus to a secondary SCSI bus includes a mechanism for detecting and resolving contention between a substantially simultaneous SELECTION operation on the primary bus and a RESELECTION operation on the secondary bus. The inventive method contemplates the bus extender arbitrating for control of the primary bus after a conflict is detected, and releasing control of the secondary bus if control of the primary bus is obtained. A target device on the secondary bus can then rearbitrate for control of the secondary bus. Once the target device controls the secondary bus, it can direct a RESELECTION signal to the bus extender, which responsively directs the signal to an initiator device on the primary bus. If the bus extender is unable to gain control of the primary bus after a conflict is detected, the SELECTION operation is allowed to proceed and the target device reattempts to assert the RESELECTION operation thereafter.

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Framingham, MA, United States of America

Fee Lee