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# Block Check Character Determination in Table Look Up Procedure

IP.com Disclosure Number: IPCOM000085262D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 42K

IBM

## Related People

Duvochel, HP: AUTHOR [+1]

## Abstract

Computation of the Block Check Character (BCC) is performed after each n-bit data character C is transmitted or received, by using tables which contain all the remainders after dividing CX/m/ by the error control polynomial P(X/m/).

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Block Check Character Determination in Table Look Up Procedure

Computation of the Block Check Character (BCC) is performed after each n- bit data character C is transmitted or received, by using tables which contain all the remainders after dividing CX/m/ by the error control polynomial P(X/m/).

A very flexible method is provided by partitioning data character C into two variable length parts. The figure shows a flow chart which illustrates the sequence of operations for computing a 2n-bit BCC.

Data character C is partitioned into parts C1 and C2 of lengths n(1) and n(2) = n-n(1), respectively. Table I contains the remainders corresponding to the 2/n1/-1 possible values of C1, and table II contains the remainder corresponding to the 2/n2/-1 possible values of C2.

The steps involved in the computation of the new BCC are as follows:
Step 1; Part C1 of data character C is added to part B1 of the old BCC (exclusive OR).

Step 2; Result of the addition gives the address of the corresponding remainder in table I. Remainder is

partitioned into parts R1 and R2 of lengths

2n-n(1) and n(1), respectively.

Step 3; R1 is added to part B2 of the old BCC.

Step 4; Result of the addition gives the first 2n-n bits of an intermediate BCC whose other n bits are provided by R2.

Intermediate BCC is partitioned into parts R'1 and R'2

of length n(2) and 2n-n(2), respectively.

Step 5; Part C2 of data character C is added to R'1. Step 6; Result of the addition gives the address of the corre...