Serial tetrad adder/subtractor in excess-3 code with decimal inputs and decimal outputs

摘要

This tetrad adder/subtractor has as the main circuit a dual tetrad subtractor 1 which processes excess-3-coded decimal numbers. This adder/subtractor thus has two input code conversion circuits 5 and 6 which convert decimal-1-of-10-coded decimal numbers into excess-3-coded decimal numbers and an output code conversion circuit 9 which converts BCD-8421-coded decimal numbers into decimal-1-of-10-coded decimal numbers. The advantage according to the invention is that a very simple correction circuit 2 can be used which only consists of 3 dual half subtractors and a residual circuit 27. The subtractions are thus carried out in a normal manner and the additions are carried out by means of subtractive addition. During the subtraction, the B inputs are the minuend inputs and the A inputs are the subtrahend inputs. The drive potential for the carry input n is supplied by the circuit 8. <IMAGE>