Low Cost Overflow Generation Device for a Multiplier-Accumulator
Original Publication Date: 1985-Oct-01
Included in the Prior Art Database: 2005-Feb-19
This article describes a method and a device to be used in a multiplier accumulator or a three-term adder assuming we know the sign of the sum of two of the three terms for generating the overflow indication and the resulting carry with a minimum number of circuits. A problem which occurs in such circuits results from the fact that additions have to be made serially and, consequently, the carry has to be propagated for each addition. In a multiplier-accumulator, the multiplier output stage provides a SUM word and a CARRY word and the multiplication result is to be added to a word M. As shown in Fig. 1, the addition of these three terms gives a SUM' word and a CARRY' word. The final result R overflows when SR' is different from SR. C is the carry generated by the addition of words SUM+CARRY. S1 is the sign of this addition.