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Determining a Check Character

IP.com Disclosure Number: IPCOM000092141D
Original Publication Date: 1968-Sep-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Wirsching, W: AUTHOR

Abstract

A check character is to be determined so that a maximum number of twenty characters comprising a maximum number of 8 bits each can be protected against commutation and the entry of erroneous data. To this end the character is read into an 8-bit register A, an 8-bit register B remaining blank in all positions. The sum-modulo 2, derived from the contents of registers A and B, is subsequently stored in register B. Having been stored in register B, the bits are shifted one position to the right. Register B is a ring shift register consisting of two parts each comprising four bit positions in each of which a ring shift to the right is made. Upon completion of shifting, the next character is read into register A. The sum is again derived from the contents of registers A and B and stored in register B.

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Determining a Check Character

A check character is to be determined so that a maximum number of twenty characters comprising a maximum number of 8 bits each can be protected against commutation and the entry of erroneous data. To this end the character is read into an 8-bit register A, an 8-bit register B remaining blank in all positions. The sum-modulo 2, derived from the contents of registers A and B, is subsequently stored in register B. Having been stored in register B, the bits are shifted one position to the right. Register B is a ring shift register consisting of two parts each comprising four bit positions in each of which a ring shift to the right is made. Upon completion of shifting, the next character is read into register A. The sum is again derived from the contents of registers A and B and stored in register B. This process continues as described until the last character is shifted in register B. Each partial register subsequently contains a hexadecimal check character. The table shows an example.

Registers Contents Bit Patterns Operations B blank 0000 0000

+

A 0111 1011

B sigma 0111 1011

shift right

B 1011 1101

+

A 3 1111 0011

B sigma 1011 0000

shift right

B 1101 0000

+

A A 1100 0001

B sigma 1001 0001

shift right

B 1100 1000

A 5 1111 0101

+

B sigma 1011 1101

shift right

B 1101 1110

Check character, hexadecimal D E.

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