8-bit aluCreated for CS63 at Earlham College
For my programming project, I have chosen to simulate an 8-bit ALU using Logic Sim. I came up with two designs, both of which were based on a one bit ALU, which I made into a module.
My first design for the 8-bit ALU was to simply string 8 1-bit ALUs together with the carry-out from from one ALU connected the carry in of the next ALU.
Based on problem 14 in Chapter 3 of Tananbaum, I made a second design with the basis that the carry-in to a stage is true if any two or three of the addend, the augend, or the carry-in of the previous stage are true.
Notice that the carry-out pin on the 1-bit ALU module is not used. Also notice that all the outputs are duplicated: 1 is right next to module and another one is on the left side of the diagram. This is so all the outputs can be easily seen at once.
I tested this new design by adding parallel bits in the A and B inputs
and checking to see if a 1 carried over into the next bit for the answer.
All bits were verified to be working correctly.
You can download the actual Logic Sim files by holding the down the
mouse over a link and choosing the SAVE AS... option.
Mark Stosberg's homepage
Last Modified December, 1997