Computing Fundamentals Tutor Adding 04: Subtraction

This video shows the adaption of a 4-bit adder circuit to do binary subtraction.

It is one of a series on binary adders, digital electronic circuits that can add binary numbers, and uses binary number theory to adapt a 4-bit adder to do subtraction, by inverting one of the inpust, and using the carry-in to add one.

This series in turn is part of a larger series that charts the creation of a simulated 4-Bit CPU, with clear explanations of what is happening at every step of the way. Following this Super-Series is a great way to gain a strong understanding of the hardware that underpins computers, and is a great learning experience for anyone interested in computing as a career or hobby.

Roadmap:

Understanding the basics of digital electronics is fundamental to the understanding of computer hardware, and this software allows you to explore that without the need for hardware, soldering irons and the such like.

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The reason you thought that the result of 3 - 10 wasn’t working is because the output uses two’s compliment. You got 1001 when you did 3-10, which in two’s compliment is -7. Your subtraction is working as it should. Great videos by the way!