Must be made using logisim

2 to 4 Decoder:

A decoder (in this case a 2 to 4 decoder) inputs a control code (2 bits for this case) which then turns on (enables) only one of the output lines (2^2 is 4). So a 3-bit input could control 8 output lines (3 to 8 decoder) and so on. Our ALU later in the term will make use of this 2 to 4 decoder as part of the microcode register decoding to control the ALU.x

8 to 1 Multiplexer (MUX):

In electronics, a multiplexer (or mux) is a device that selects one of several analog or digital input signals and forwards the selected input into a single line. A multiplexer of 2ⁿ inputs has n select lines, which are used to select which input line to send to the output. The MUX below is 8 to 1 MUX which requires 3 select lines which represent the address (0 to 7) to select which data input line is forwarded to the single output line. One use of a MUX is to filter which registers data is presented on the internal bus on the input side of the ALU. It will take 8, 8 to 1 MUXes to select from 8, 8-bit registers (this is what we will later be building).

8-Bit Comparator

This basic comparator circuit does a bitwise comparison between two input bytes (for an 8-bit comparator) to determine if the two inputs are bit by bit equal. Below is a 4-bit comparator; you are to extend this to an 8-bit comparator to compare to 8-bit input bytes.

8-bit wide, 1 bit Left-Right Shifter:

This circuit SHIFTs the bits one bit to the left or right depending upon the value of the control line C (C = 1 is left shift, C = 0 is right shift). A 0 is padded on the right most bit for a left shift, or the left most bit for a right shift. This is the basis for a more common circuit called a Barrel Shifter which can shift multiple bits in either direction. Note that the 0 subscripted bits are the right most bits in an input word so shifting D1 to S0 is a right shift.