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System Diagnostics Through Complete Field Replacement Units

IP.com Disclosure Number: IPCOM000034820D
Original Publication Date: 1989-Apr-01
Included in the Prior Art Database: 2005-Jan-27
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Eckel, JW: AUTHOR [+4]

Abstract

A technique is described whereby standard logic circuit hardware is used to logically isolate circuit board problems from the rest of the system. The concept supplies diagnostic input and monitors the output, eliminating the need for special-purpose diagnostic circuitry. Typically, there are two standard practices for implementing diagnostics in an electronic system. One practice is to build two identical copies of each of the logic subassemblies and then to continually compare the two outputs. If the outputs do not agree exactly, a problem may require addressing either automatically or through manual intervention. This costly method requires doubling the logic and runs the exposure of failures occurring in the diagnostic logic itself.

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System Diagnostics Through Complete Field Replacement Units

A technique is described whereby standard logic circuit hardware is used to logically isolate circuit board problems from the rest of the system. The concept supplies diagnostic input and monitors the output, eliminating the need for special-purpose diagnostic circuitry. Typically, there are two standard practices for implementing diagnostics in an electronic system. One practice is to build two identical copies of each of the logic subassemblies and then to continually compare the two outputs. If the outputs do not agree exactly, a problem may require addressing either automatically or through manual intervention. This costly method requires doubling the logic and runs the exposure of failures occurring in the diagnostic logic itself. A second practice is to build reduced diagnostic circuitry in parallel with the more critical system circuitry and to use this circuitry to monitor circuit operation. Although this second practice is less costly than the first, it could be less effective in performing diagnostics. This is because not all functions of the unit under test are diagnosed and those that are under test will be checked only under certain conditions. The concept described herein implements diagnostics without duplicating any of the system logic. It provides a method of isolating the inputs to each logic subassembly from the rest of the system. A method is then provided for monitoring all the inputs and outputs from each logic subassembly. Monitoring the outputs assures that the proper function was performed. The concept provides complete control over the inputs. This allows any number of combinations of inputs to be supplied and will be able to check the operation of a subassembly, under all possible conditions. The checking includes normal operating conditions, as well as any number of possible error conditions. The electronics portion of a system being diagnosed is divided into a number of circuit board sections, with each section containing up to 300 large-scale integrated (LSI) logic packages. Each circuit board is connected to the rest of the system through a number of pluggable cables and are designated as field replaceable units (FRUs). The diagnostic hardware on each circuit board consists of a microcontroller with: a) its own support logic, b) multiplexers for is...