Digital Equipment Corporation

Compaq Computer Corporation, Inc.

Keith Childs

Fee Lee

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 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.

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Whitinsville, MA, United States of America

Keith Childs