Abstract: This invention relates to a visual indication system for a field replaceable unit. The system includes two or more visual indicators on a face of the field replaceable unit (FRU), each indicator having a unique shape and being switchable between an on state and an off state. Diagnostic and administrative control within the FRU functions to monitor overall operation of the FRU and, under the control of Network Operations Systems, selectively turns on or off the visual indicators to reflect status of the FRU.

Abstract: A hardware simulator comprises a plurality of interconnected programmable logic devices (20) which are connected via a data bus (22) and a control bus (24). Address signals on control bus (24) are read by an interconnect logic block (18) associated with each device to selectively link the output latches and input latches of the devices (20) to the data bus (22). Accordingly, a series of signal transfers is carried out between the devices simulating the hardware. The interconnect logic blocks may be programmed to provide whatever connections between devices are required.

Abstract: An asynchronous serial data receiver for receiving a stream of data bits, characterized by a plurality of shift registers (54) into which samples corresponding to points within said data bit stream are read, different shift registers (54) holding a different set of said samples, said points being separated by most one half of a data bit period, and a decoder (60-90) responsive to said samples held in said shift registers (54) for recognizing points of known phase within said data assessed relative to which samples which corresponding to points within said data bits may be identified for reading. The invention provides a high speed serial receiver which is particularly suitable for use within disc drives and data storage and retrieval systems in general. The serial data receiver of the present invention does not require a clock synchronized with the incoming data.