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Cyclic Redundancy Check for Variable Bit Code Widths

IP.com Disclosure Number: IPCOM000082335D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Brodd, WD: AUTHOR [+2]

Abstract

One generalized format utilized for the block transfer of information in a serial-by-bit fashion and for error checking of the transfer function is of the following form: where: 1) The delimiter is a unique sequence of multiple bits used to identify the first data bit and the last bit of the checking redundancy field. 2) The data field contains the information to be transferred and may be a variable number of bits in length. In general, the data field will be a fixed number of bits or an integer modulus of some predetermined code width. 3) The checking redundancy field is of fixed length and represents the remainder derived by the division of the data field, by a specified polynomial via modulus 2 arithmetic.

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Cyclic Redundancy Check for Variable Bit Code Widths

One generalized format utilized for the block transfer of information in a serial-by-bit fashion and for error checking of the transfer function is of the following form: where: 1) The delimiter is a unique sequence of multiple bits used to identify the first data bit and the last bit of the checking redundancy field. 2) The data field contains the information to be transferred and may be a variable number of bits in length. In general, the data field will be a fixed number of bits or an integer modulus of some predetermined code width. 3) The checking redundancy field is of fixed length and represents the remainder derived by the division of the data field, by a specified polynomial via modulus 2 arithmetic.

The most generalized error detection implementation of the above at the "sink" (receiving) termination, is to perform a similar division on the received data and checking redundancy fields, and then test for a predetermined and predictable value following the last bit of the checking redundancy field. If the predetermined value does in fact result, an error-free transfer is indicated.

With the use of suitable storage or delay means at the sink termination, it is possible to detect the ending delimiter and test for the predetermined value, following receipt of the last bit of the checking redundancy field. However, providing such storage or delay means can increase the cost of the sink termination equipment.

There is an alternative approach available, in which one or more bits of the ending delimiter may be included in the checking calculation prior to receipt and resultant detection of the entire ending delimiter sequence. Under these conditions, tests are simply made for an alternative predetermined value...