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Cable Wrap Test With Bit Shift

IP.com Disclosure Number: IPCOM000048488D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Groot, AJ: AUTHOR [+3]

Abstract

In the past, a cable wrap test consisted of passing variable data over cable and storing the data in a register long enough to allow read back of the data. If the data read does not compare with the output data, and if the failure rate of the register is low in comparison with the cable failure rate, then a defective cable is indicated. In order to detect all opens and shorts, it is usually necessary to run "n" tests, where "n" is the number of bits in the bus. A single "0" is inserted in a field of n-1 "1's". The "n" passes are required in order to place the single "0" in each of the bit positions.

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Cable Wrap Test With Bit Shift

In the past, a cable wrap test consisted of passing variable data over cable and storing the data in a register long enough to allow read back of the data. If the data read does not compare with the output data, and if the failure rate of the register is low in comparison with the cable failure rate, then a defective cable is indicated. In order to detect all opens and shorts, it is usually necessary to run "n" tests, where "n" is the number of bits in the bus. A single "0" is inserted in a field of n-1 "1's". The "n" passes are required in order to place the single "0" in each of the bit positions.

A simple means has been developed which makes it possible to reduce the number of test passes to "n"/2. The unique characteristic of the new cable wrap test results from the fact that the data register used is a free-running shift register. A known number of shifts occur between the loading of a byte and the reading of the byte. This is advantageous because two cable wires must be operational in order to complete a single wrap test. For example. as shown in the figure, if eight data bits are being tested, and a two-bit shift occurs, then only four output bytes are required in order to test the entire cable. In the case illustrated, data output on bit 0 would return on bit 2, bit 1 on bit 3, etc. The output data patterns would be B(0111 1111), B(1011 1111), B(1111 0111), and B(1111 1011). The patterns returned would be B(1101 1111), B(111...