Abstract: In a pulse width modulated read signal channel for an optical disk drive, a data-transition threshold is maintained for data detection by a threshold tracking circuit that estimates the amplitude centerline data-transition threshold from the most recent maximum and minimum values of the read signal waveform. To improve the accuracy of the response of the centerline estimator, the threshold is increased or decreased based on the phase error at each read signal transition through the data-transition threshold. In addition, defects in the optical recording media are detected, and a defect present signal is used to inhibit the transition phase error input to the centerline estimator. This prevents the estimator from moving the threshold to an incorrect stable level. In addition, the defect present signal boosts the error feedback in the centerline estimator. The estimator then more quickly follows the read signal waveform.

Abstract: A programmable I/O bus adapter for interfacing and controlling two data processing systems having dissimilar and incompatible architectures. The programmable I/O bus adapter is capable of controlling the I/O bus and adapters of each of the two data processing systems. Simultaneously, the I/O bus adapter provides for interfacing and communication between the two dissimilar data processing systems. Interfacing from the bus adapter to each data processing system is provided by circuitry provided on integrated circuit chip sets specifically designed to interface with each system. The interfacing circuitry is enabled to convert signals between each system to allow for communication. Communication paths couple the adapter to the I/O bus of each system. The ability to access and control an I/O bus and adapter of each system is provided by a microprocessor having microcode instructions stored in programmable memory.

Abstract: A digital phase lock loop channel is provided for threshold detection of a pulse width modulated binary data stream that has negative and positive transitions defining one binary state of the data stream. A threshold-establishing and transition-detecting network receives this data stream and provides a first output of one polarity corresponding to the detection of a positive transition, a second output of an opposite polarity corresponding to the detection of a negative transition, and a time-of-arrival output corresponding to a positive and a negative transition. A first and a second digital PLL is provided, each PLL having a transition input, a time-of-arrival input, a phase-error input, a phase error output a data-valid output, and a data output. Each PLL has an internal digital phase detector network connected to receive its transition input and its time-of-arrival input, and each PLL is operable to generate the phase error output therefrom.

Abstract: A bus-to-bus adapter is provided for coupling the input/output bus of a first data processor to the input/output bus of a second and different type of data processor. The adapter enables the transfer of data and messages from the first processor to the second processor and vice versa. The adapter includes a buffer storage unit and control logic for enabling multiple data buffers to be provided for enabling multiple independent data transfer operations to be performed in a concurrent manner. The control logic also includes a mechanism for allowing the reading out of data from a data buffer to begin before such data buffer has received all of its incoming data. The adapter further includes a programmable service time allocation mechanism for limiting message service time relative to data transfer service time and for providing different amounts of data transfer service time for different ones of the multiple data buffers.