Question

PROBLEM STATEMENT The mini-calculator will use a small ALU to perform arithmetic operations on two 4-bit values which are set using switches. The ALU operations described below are implemented with an Adder/Subtractor component. A pushbutton input allows the current arithmetic result to be saved. An upgraded mini-calculator allows the saved value to be used in place of B as one of the operands. The small ALU that you will design will use the 4-bit adder myadder4 to do several possible operations. The circuit will take two 4-bit input values from switches, a3 a2 al a0 and b3 b2 b1 b0, to be the operands. Four switches, p3, p2, pl, and p0 will specify the arithmetic operation. These four bits can be interpreted as an operation code. The operations are specified in the table below. (Note that p3-0 for all table entries below. A new feature for p3-1 will be added in the lab.) The output will be a 4-bit value r3 r2 r1 r0 and three single bit outputs: a carry out, an arithmetic overflow, and a zero result bit. Output R r3 r2 r1 r0 R-A+B R-A+B+ Add and Increment R-A-B-1 Subtract and Decrement Notes Op-Select Input Operation Add 0010 0011 01 0 0 0 101 01 10 0111 R-A-B R-A R-A+1 R A-1 R-A Subtract Transfer A Increment A Decrement A Transfer A (duplicate-note that this can be done in 2 wa 1. Be sure you understand 2's complement representation of signed numbers. The 4-bit adder can be used for adding or subtracting since (-B) represented in 2's complement form can be added to A to get A-B-A+(-B). The bit operations for addition are the same for both unsigned addition and signed addition using 2's complement representation. This is why 2's complement representation is so widely used. The bit pattern result is the same for both, but the interpretation of the value of the bits will be different for signed and unsigned numbers. Fill in the table below for your adder Y inputs and carry-in input for each of the four operations listed. The operations are specified by pl and pO when p3-p2-0. The first entry has already been completed for you. Adder Adder Adder Notes Operation 4-bit X inputs4-bit Y inputs Carry-in p3 p2 pl pO a3 a2 al a0 a3 a2 al a0 a3 a2 al a0 a3 a2 al a0 a3 a2 al a0 b3 b2 b1 b0 b3 b2 bl b0 R-A+B Add 0 0 01 0010 0011 R-A+B+1 Add and Increment R-A-B-1Subtract and Decrement R-A-B Subtract The myadder4 component from the previous lab will be used to perform the ALU's addition. The ALU A input will be connected to the adder X input, and the adder S output will be the ALU R output. The adder Y input and carry-in to the adder will depend on which operation is selected, as defined by the table above..

Answer 1

o 1 1 PO 4A blt Adde PA