Re: ALU Implementation - the road traveled thus far
Posted by WBahn on Jun 26, 2019; 10:09pm
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/ALU-Implementation-the-road-traveled-thus-far-tp4033278p4033351.html
Are you sure you have this mapping correct?
Look at the specifications for the 4-way Mux carefully.
There's a reason that I keep harping in incremental development. Start out with just the control signals for the x input and check that you get what you want on the output of the Mux for all four combinations. It makes it easy to test all possible control inputs and fix any problems. Then add the y input and check it. Then add the adder and ander and check that. Then add the output Mux and check that. Then deal with the two flag bits. When you throw everything together and then try to test the whole thing, when there's an error you have too many possible places where you could have gone wrong and you end up floundering around.
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/ALU-Implementation-the-road-traveled-thus-far-tp4033278p4033351.html
Are you sure you have this mapping correct?
Look at the specifications for the 4-way Mux carefully.
There's a reason that I keep harping in incremental development. Start out with just the control signals for the x input and check that you get what you want on the output of the Mux for all four combinations. It makes it easy to test all possible control inputs and fix any problems. Then add the y input and check it. Then add the adder and ander and check that. Then add the output Mux and check that. Then deal with the two flag bits. When you throw everything together and then try to test the whole thing, when there's an error you have too many possible places where you could have gone wrong and you end up floundering around.
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