Author: Yuzhe Ding (yd160); Aohua Zhang (az147) Date: 09.23.2021

32-bit General Adder Design

• 8-bit Ripple Carry Adder (RCA) implemented with 8 consecutive Full Adders (FA) connected by Cin and Cout
• 16-bit Carry Select Adder (CSA) implemented with 3 8-bit RCAs and 1 8-bit 2-to-1 multiplexer (Mux)
• 32-bit CSA consists of 3 16-bit CSA and 1 16-bit 2-to-1 Mux
• Calculate the overflow by implementing xor operation between the Cout and Cin of the most significant bit (namely the 31th bit of the adder)
• Extract the least significant bit (LSB) of ctrl_ALUopcode as the Cin of the entire 32-bit CSA
• Use the LSB of ctrl_ALUopcode to determine whether to invert the input data_operandB

32 bitwise And/Or

• Put 32 1-bit And/Or in parallel

Barrel Shift left (logic)

• Use five level mux stacks, which shift 1, 2, 4, 8, 16 bits respectively

Barrel Shift right (arithmetic)

• Use five level mux stacks, which shift 1, 2, 4, 8, 16 bits respectively

5-to-32 Decoder

• First implement a 2-to-4 decoder with an Enable input
• Then use 2 2-to-4 decoders to construct 3-to-8 decoder with the Enable input connected to the MSB of the input
• It's the same for 4-to-16 and 5-to-32 decoder

Tristate Buffer

• I use the constant 1'bz to implement the tristate buffer
• Use the output of the decoder to enable the tristate buffer to select which data appears on the final output