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owl [soylentnews.org] writes:

In this post, I discuss the circuitry that controls the ALU, generating the appropriate control signals for a particular operation. The process is more complicated than you might expect. First, a machine code instruction results in the execution of multiple microcode instructions. Using the ALU is a two-step process: one microcode instruction (micro-instruction) configures the ALU for the desired operation, while a second micro-instruction gets the results from the ALU. Moreover, based on both the microcode micro-instruction and the machine code instruction, the control circuitry sends control signals to the ALU, reconfiguring it for the desired operation. Thus, this circuitry provides the "glue" between the micro-instructions and the ALU.

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