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Building the ALU

A project log for CPU-001

16-instruction, 12-bit Asynchronous CPU

konstantinKonstantin 05/31/2020 at 18:211 Comment

In the beginning, there were prerequisites...

6x 74HCT08 (AND Gate)

3x 74HC32 (OR Gate)

2x 74HCT04 (2x Hex inverters for a total of 12)

Guess what these form..

One. XOR Gate. (well twelve but its still yewsless)

             How will this help us in our addition journey? Well, the outputs of all gates except OR will also be interfaced with buffers to feed back into registers A and B (XOR into A, AND/NAND into B, depending on opcode,) which when combined with shifting will allow for addition in a maximum of 13 steps (recursive XOR & left-shift AND when fed back into A,B becomes the sum in 2^bit width + 1 for some reason,) but can be reduced with conditional jumps (i.e. break loop if B=0; addition completed.)

Once I build the registers, of course

Discussions

Konstantin wrote 05/31/2020 at 18:23 point

P.S. This takes way less space than an equivalent Full Adder (especially if all gates were made from transistors), while introducing more functionality. I didn't want to spend time making a real adder board, and didn't want to solder in black boxes, either.

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