Digital Equipment Corporation

Jesse B Lipcon

Barry A Maskas

David K Morgan

A digital data processing system includes a plurality of processing subsystems, each including an adapter for enabling transfers between the resident subsystem and other subsystems. The adapter includes a master section which enables transfers of data initiated by the subsystem between the input/output bus and the higher level communications mechanism, a slave section which enables transfers of data between the higher level communications mechanism and the input/output bus initiated by another subsystem and an interprocessor communications mechanism for enabling the subsystem and other subsystems to communicate to thereby enable the other subsystems to perform control operations in connection with the subsystem.

Bus adapter unit for digital processing system

A self-testing memory simultaneously writes test patterns into the memory banks of the memory, simultaneously compares the contents of one of the memory banks with the contents of the other of the banks, and records errors when the contents of the one memory bank differ from the contents of the other banks.

Self-testing memory

An expandable memory connected to a central processing unit includes several memory modules which transfer configuration signals serially to the central processing unit by way of an interface circuit. The interface circuit also selects ones of the memory modules for access by the central processing unit according to the configuration signals.

Arrangement for expanding memory capacity

A precision voltage and current source for use, for example, in a transceiver for a carrier-sense multiple access communications network using collision detection wherein the use of one or more precise threshold voltages is required. The threshold voltage(s) is (are) created by a current source which pulls a current through a precise resistive load to yield a precise voltage. A power supply with regulated voltage drives the current source. A feedback voltage from the current source, proportional to the output current of the source, is compared with a reference zener diode voltage; the difference, or error, voltage controls the regulator to drive the regulated power supply voltage in the direction which drives the error voltage to zero. The precise resistive load is preferably formed of two resistors in series. A first threshold voltage is developed across one resistor, corresponding to the average signal level required for receiving signals on the network. A second threshold voltage is developed across the series pair of resistors, corresponding to the minimum average signal level which would be produced by a collision.

Precision setting of currents and reference voltages

A transceiver for a carrier-sense multiple access communications network using collision detection for controlling access to the network, and utilizing industry standard emitter-coupled logic (ECL) circuits in its receiver and transmitter. The transmitter output stage is an ECL current source. To prevent saturation of the transmitter output in the event of a collision, due to the voltage swing exceeding the compliance limit of the ECL current source, with a resulting failure of the collision detection mechanism, the power supply for the transmitter output stage supplies voltage in a first range of about -5 to -10 volts, while the power supply for the receiver input and collision detection circuits supplies voltage in a second, contiguous range of zero to about -5 volts. This permits the transmitter output to swing about 6-7 volts without exceeding the compliance limit of the current source, so that the collision is detectable by the collision detection circuits.

Transceiver for local network using carrier-sense multiple

A tester for the collision detector of a transceiver for a multiple access data communications network using carrier-sense collision detection for controlling access to the network. A squelch circuit is employed in the transceiver's transmitter for enabling and disabling the transmitter output. An end-of-transmission detector monitors the squelch circuit to detect the termination of a transmission. Upon termination of a transmission, a collision simulator circuit supplies to the transceiver's receiver a signal of predetermined amplitude and duration, to simulate the input the receiver gets when a collision actually occurs. If the receiver is working properly, it signals a collision to the host (i.e., computer, terminal, etc). If it does not receive the collision signal at the appointed time, the host knows that either the transceiver's collision detection circuit or the tester is not working.

Tester for collision-detect circuitry

A self-zeroing, drift-free analog-to-digital conversion system is disclosed in which a single amplifier is shared between an analog-to-digital converter circuit and a sample-and-hold circuit. The offset errors generated by the sample-and-hold circuit cancel with the offset errors generated by the analog-to-digital converter circuit since the circuitry introducing the offset errors is shared. As a result, system offset errors are negated and the system enables changing from a unipolar to bipolar input range without inclusion of any additional circuitry. Usage of a gain preamplifier is provided with no corresponding system offset errors being introduced. moreover, usage of a differential-input gain preamplifier is also provided, with the self-zeroing feature resulting in greatly improved common-mode rejection.

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Harvard, MA, United States of America

Jesse B Lipcon