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# alu - Problems 1 Begin by drawing the schematic of the the...

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Last updated: 11/4/2006 ECEn/CS 224 ALU Homework Solutions Background In the LC-3 there is an ALU which performs the functions PASS, ADD, AND, NOT. The last three should be self-explanatory. The PASS function simply passes the first input through to the output. Assuming inputs A and B as well as control signals C1 and C0, the behavior of the ALU is outlined in the table below. Control Function Select Function C1 C0 0 0 PASS Out = A 0 1 ADD Out = A + B 1 0 AND Out = A • B 1 1 NOT Out = A’ One way to build an ALU is to build a bit-slice. That is, you build one bit worth of ALU first. Then, you combine n of those together to make an ALU that works on n-bit values. Further, a good way to design such an ALU is to simply implement each function independently (AND, ADD, NOT, PASS) and then combine their outputs together using a 4:1 MUX.

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Unformatted text preview: Problems 1. Begin by drawing the schematic of the the full adder as described in section 8.6 of the text. A B Cin A A B Cin Cin B S Cout Last updated: 11/4/2006 2. Now incorporate your single bit adder into a single bit ALU. This ALU contains a 4-to-1 mux with inputs of A , A+B (addition), A AND B , and NOT A . Draw the Logic Diagram for this single bit ALU. The inputs should include A , B , Cin , and C[1:0] (control). The outputs should include Out and Cout . 3. Now draw a symbol for this 1-bit ALU and show how you would combine 4 of them into a 4-bit ALU. A(1) B(1) R(1) A B Cin Cout Ctrl(0) Ctrl(1) A(2) B(2) R(2) A B Cin Cout Ctrl(0) Ctrl(1) A(0) B(0) R(0) A B Cin Cout Ctrl(0) Ctrl(1) Cin Ctr Cout A(3) B(3) R(3) A B Cin Cout Ctrl(0) Ctrl(1) Out Out Out Out A B Cin S Cout 00 01 10 11 A B Cin C[1:0] Out Cout...
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alu - Problems 1 Begin by drawing the schematic of the the...

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