NOTE: Click STOP first, then START to start the animation.
CPU Central Processor Unit
The CPU is the heart of the computer and is composed of five basic components. The RAM is created from combining latches with a decoder. The latches create circuitry that forms the memory, individual memory locations being controlled by a decoder. The Instruction register, the Program Counter and the Accumulator are registers that are special memory locations capable of being accessed fast. The Buses are bundles of tiny wires that carry data between components. The address, the data and the control buses are the most important. The Arithmetic Logic Unit performs all the mathematical calculations of the CPU. It is composed of complex circuitry and its functions include adding, subtracting, multiplying and dividing binary numbers. The Control Unit directs the flow of instructions and data within the CPU. It is built of other selection circuits such as decoders and multiplexors. Inputted instructions tell the CPU to perform actions on inputted data. The data and instructions are represented by binary code. Both inputs are stored in the memory and the CPU follows a cycle of fetching an instruction, decoding it and executing it.
An instruction is transferred from the memory to the Instruction Register along the data bus. In the Instruction Register the unique bit patterns of the instruction are sent to the Decoder. The Decoder recognises which operation the bit pattern represents and activates the correct circuitry to perform the operation. This may involve reading data from memory, storing data in memory or activating the Arithmetic Learning unit to perform a mathematical operation. Once performed the cycle begins again. The Program Counter holds the address of the current instruction and each time an instruction is completed the program counter is advanced by one memory location. The Accumulator acts as temporary memory store whilst the processes are taking place. The simulation represents adding of two pieces of data
Stages of animation
1. The value 3 is loaded into the Accumulator.
2. The value 3 is stored in memory location 11
3. The value 6 is loaded into the Accumulator.
4. The value 6 is stored in memory location 12
5. Load the value of memory location 11 into the Accumulator.
6. Add the value of memory location 12 to the Accumulator.
7. Store the value of the Accumulator in memory location 15.
8. Halt execution