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Carry Dependent Sum

IP.com Disclosure Number: IPCOM000094922D
Original Publication Date: 1965-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Bearnson, LW: AUTHOR [+2]

Abstract

This circuit generates a sum output signal S(n) of a stage n which is dependent upon a carry output signal C(n) from the same stage. If the carry is generated erroneously, this causes the sum to be erroneous also. Thus. if a parity check circuit is used to detect errors in the sum, it also detects errors in the carry.

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Carry Dependent Sum

This circuit generates a sum output signal S(n) of a stage n which is dependent upon a carry output signal C(n) from the same stage. If the carry is generated erroneously, this causes the sum to be erroneous also. Thus. if a parity check circuit is used to detect errors in the sum, it also detects errors in the carry.

Carry generator 10 can be of the ripple carry or carry look-ahead type. The circuitry shown is associated with stage n of the adder and is repeated for each stage. Carry C(n-1) is a carry from the next previous stage. Carry C(n) is the carry generated by stage n. The bit inputs are represented by A(n) and B(n) which are to be added in the stage n, giving the sum S(n) which,in conjunction with the carry C(n), fully expresses the addition operation for stage n.

A T(n) output indicates that stage n transmits a carry. T(n) is equal to A(n) + B(n). A G(n) output indicates that the stage generates a carry and G(n) is equal to A(n) B(n). The transmit and generate carry functions are used in generator 10 and are also utilized in the sum logic shown. The generate function is formed by And 12. The transmit function is formed by Or 14. The equation for the carry- dependent sum is given by:

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And's 16, 18, 20 and 22 each correspond to the terms of the above equation for the sum S(n). The Or function of the terms of this equation is accomplished in Or 24 which receives the outputs of all And's 16. 18, 20 and 22.

C(n+1), C(n), C(...