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Partial Construction
"Computers are a glorified, high-class, very fast but stupid filing system. " - Richard P. Feynman
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The Clock
The Register
Where it comes together
The Clock
In everyday life clocks synchronize our world. Clocks allow for people to work together and reach a common goal. Imagine working within a team where each person is doing something differently, it is only when they come together where their goal can be achieved effectively. Clocks, like a great leader, will keep all operations in check and encourage organized communication through their system.
Richard Feynman describes the computer as a filing system, something that handles data by electrical impulses. The data being sent must be synchronized otherwise it will be filed in irrelevant places. Computer memory is sequential, meaning the memory is a function of its present inputs and the sequence of its past inputs. When the data being sent is synchronized with a clock or "enable" every event happens at the same time. The higher the clock speed, the more data can be filed within a given time.
This 555 Timer is arranged to operate in an Astable state meaning that it is alternating between a High and Low state serving to set the clock's speed at a specific frequency that is found below. These two values for HIGH and LOW should be very close in our case because we are setting a precise clock speed. With a simple swap of the first resistor we can allow for HIGH to last longer
The Blue LED is Q, the Yellow LED is Qnot
The second 555 Timer in this section operates in a Monostable state meaning that the output can be in only one state unless otherwise told to switch. This allows the user to manually implement a single clock cycle which can be useful for debugging or just understanding the operations taking place throughout the computer.
Although this manual clock advancement can be achieve with just a current limiting resistor, LED and tactile button, we make use of the SR Latch within the 555 Timers integrated circuit. A tactile button allows current to flow through when the two metal contacts touch, when this occurs the two contacts can bounce and send unwanted clock advancements which leads to errors. With the SR Latch, we toggle the button to set and once the latch is set, the bounces from the button will have no effect on Qnot (The output) because the Latch will remember the state it is set in until S (Set) is activated. In our case, R is normally High and is grounded when the button is activated allowing the Latch to set from the potential across the Comparator where the LED on pin 3 is set High (Qnot) and is on for the amount of time it takes to Set again determined by the RC Time constant on pin 6 and pin 7 which is a very small amount of time...
(R * C = 1 MΩ * 0.1μ F )= One tenth of a second High just enough for a single pulse.
The Final Product
The completed Clock Module operates in two methods..
In the first way, the final clock pulse (Top right yellow LED) is exactly that of the Astable pulse and can be slowed down by the potentiometer.
In the second way, the Monostable clock pulse is activated by the switch so that a pulse can be advanced manually. See in the video what happens after the switch is activated.
The 3 Logic Gate ICs are intended to switch between the Astable and Monostable states when directed and affect the final clock pulse.
The Logic Block
This combination circuit is designed to select between the two modules mentioned above. Below is the process of how circuits like these are designed.
Registers
Registers, How Computers Receive and send information.
In this module, Two independent Registers are used to intermittently store data during the execution of a program. They are named by the amount of Bits they can store, both Register A and B are 8-Bit Registers as each Integrated Circuit can store 4-Bits.
Inside of each IC, are 4 D-Type Flip Flops which on their own store one Bit of data but when put together can store more Bits. D-Type Flip Flops rely on two inputs and a Clock Input which opens a "Gate" when high allowing new information to enter. The clock pulse is essential for synchronizing these operations.
Attached to each register at pin 9/10 is the "Data Enable " or "Load" pin . When grounded, this loads the register with data present at their inputs (1D-4D). When load is off, data is kept as long as the chip is powered and can be accessed by the Bus Transceiver (Data Control) to be sent throughout the computer (1Q-4Q) via the bus (bottom left).
Register A/B operate in the exact same manner, with the only difference being that they can store separate data which can be sent to the Bus for use throughout the computer.
Refer to the images below for step-by-step operation
Where it comes together
The CPU as a unit
A Computer's Central Processing Unit or CPU is commonly refereed to as the "brain" of the system. Where instructions given by a computer program are executed. The program itself is fed through parts of the CPU and from there sent to different parts of the computer. For example, when touching something very hot, the feeling is received and sent through your nervous system and understood by the brain. The brain then tells your muscles to retract and stay away from the hot surface. This is a simple I/O operation, the computer as a whole operates in a similar way to the human nervous system.
One of earliest CPU's is the Intel 8008 featured in the image without its formal dual in-line package. This is an 8-Bit CPU containing 3,500 transistors with a max clock of 200 kHz to 800 kHz. The most amazing feat by Intel is the fabrication process that went into this 10µm die.
The Registers/ALU and Clock are only a small but essential part of the CPU and can be found below.
Intel 8008 Die, 1972
The Photo-Lithographic Process
This is the absolute most fascinating process and is a true display of innovation and engineering. As an engineer, your job is to innovate and make the world a better place. Another obsession in engineering is scalability, making devices smaller and scaling big ideas like, "What if the ENIAC could fit on my desk instead of taking up the entire room?" From problems come solutions and the solution to large and power hungry circuits is Photo-Lithography. I like to think of it as the "Reverse projector". Instead of making images larger from smaller slides, it makes images smaller from larger slides. This allows for many layers within an integrated circuit's die to be cast down into an extremely small image which can be exposed, set, and stacked to build circuits on a silicon wafer. When repeated the result is a large wafer with millions of dies ready to be cut by a diamond saw and placed in its package.
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