DATA PROCESSOR HAVING UNITS CARRY AND TENS CARRY APPARATUS SUPPORTING A DECIMAL MULTIPLY OPERATION

摘要

A data processing system executes a decimal multiply instruction by storing the product of a multiplier decimal digit and a multiplicand decimal digit in a read only memory and storing partial product decimal digits in a register. The units product decimal digit is read from the read only memory during one cycle and added to a partial product decimal digit. resulting units carry is stored in a units carry flop. The tens product decimal digit is read from the read only memory during another cycle and added to a higher order partial product decimal digit. A resulting tens carry is stored in a tens carry flop. A multiplexer selects the output of the units carry flop for adding the units carry during the next units cycle in which the next units product decimal digit is added to the higher order partial product decimal digit. The multiplexer selects the output of the tens carry flop for adding the tens carry during the next tens cycle in which the next tens product decimal digit is added to a next higher order partial product decimal digit.