Contents
What does the ALU carry out?
The ALU carries out basic arithmetic and logic operations, and the control section determines the sequence of operations, including branch instructions that transfer control from one part of a program to another.
How is multiplication performed in ALU?
When used for multiplication: MD initially contains the multiplicand and Lo contains the multiplier; Hi is initially 0. each step shifts Hi/Lo to the right. the ALU either adds the MD register (the divisor) to its Hi input or passes the Hi input through unchanged depending on the low-order bit of Lo.
How does an ALU add?
The ALU can also perform other operations. It can increment, add 1 to word A, or decrement, subtract 1 from it. By complementing (inverting) the logic value of individual bits of the data word A and adding 1 to the result, it is possible to use twos complement arithmetic to perform subtractions.
Why does an ALU always output both carry and overflow?
Because 7 (0111) + 7 (0111) = 1110, which in 4-bit twos-complement is -2. Overflow occurs when the size of the inputs is such that there is a carry which changes the most-significant sign bit. The ALU will always output both carry and overflow, but both only makes sense when the operation is add or subtract.
How do I change the hand icon in alu6?
Open ALU6.circ in Logisim, then double-click on the 4-bit AND component in the left drop-down menu. The 4-bit AND circuit should open up for you. Select the Hand icon in the top-left of the Logisim window, then click on the data inputs to change their values.
How many control lines does an Alu have?
The ALU will take in two 32-bit values, and 2 control lines. Depending on the value of the control lines, the output will be the addition, subtraction, bitwise AND or bitwise OR of the inputs. Schematically, here is what we want to build: Note! This is an interface for the ALU: what goes in, what comes out.
How is the ALU used in the Multi-Precision algorithm?
Since the size of a fragment exactly matches the ALU word size, the ALU can directly operate on this “piece” of operand. The algorithm uses the ALU to directly operate on particular operand fragments and thus generate a corresponding fragment (a “partial”) of the multi-precision result.