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Browse Prior Art Database

Backdoor Window Generator

IP.com Disclosure Number: IPCOM000046878D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Bardell, PH: AUTHOR [+2]

Abstract

When a shift register latch (SRL) array of M shift register strings arranged in N rows is repetitively loaded with pseudo-random binary numbers from this linear feedback shift register (LFSR), the array has the property that each of 2mnl possible non-zero binary patterns is seen through a non-movable (m x n) window in 2mnl sequential reloadings of the array by the LFSR. The backdoor window generator will be a maximal-length linear-feedback shift register of m x n stages. A window of size m x n will require 2mnl unique reloadings of the array before all possible non-zero patterns cycle under the fixed window. Assume that 2mnl >> N and that N is relatively prime to 2mnl.

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Backdoor Window Generator

When a shift register latch (SRL) array of M shift register strings arranged in N rows is repetitively loaded with pseudo-random binary numbers from this linear feedback shift register (LFSR), the array has the property that each of 2mnl possible non-zero binary patterns is seen through a non-movable (m x n) window in 2mnl sequential reloadings of the array by the LFSR. The backdoor window generator will be a maximal-length linear-feedback shift register of m x n stages. A window of size m x n will require 2mnl unique reloadings of the array before all possible non-zero patterns cycle under the fixed window. Assume that 2mnl >> N and that N is relatively prime to 2mnl. (Since each reloading of the array requires N sequential M-bit words from the generator, 2mnl unique reloads cannot be obtained unless N is relatively prime to 2mnl. If this criterion is not met in the actual array, one or more rows of "imaginary" SRLs are added to the array until it is met. What is wanted is that N, the number of sequential words taken from the generator for each reload, be relatively prime to 2mnl. Each added row of "imaginary" SRLs increases the number of words required by one and increases the number of shift clock cycles by one. The extra words merely shift off the bottom of the array.) The array is connected to the backdoor generator so that each column of the array is fed by a phase-shifted version of the generator sequence and such that the phase shift for each column lies a distance of n shifts from its left-adjacent neighbor column, where n is the desired depth of the window. The figure shows the construction of a backdoor generator for an array of 5 columns by 3 rows when a 2 x 2 window is desired. A 4-stage linear feedback...