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An address bus is a bus that is used to specify a physical address. When a processor or DMA-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus (the value to be read or written is sent on the data bus). The width of the address bus determines the amount of memory a system can address.
A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to determine its operation. The technique was developed to reduce costs and improve modularity, and ...
The memory controller manages access to memory using the memory bus or a system bus, or through separate control, address, and data buses, to execute the program's commands. The bus managed by the memory controller consists of multiple parallel lines, each representing a binary digit (bit).
In computer architecture, a control bus is part of the system bus and is used by CPUs for communicating with other devices within the computer. While the address bus carries the information about the device with which the CPU is communicating and the data bus carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices.
The hardware of the system is arranged so that devices on the address bus will only respond to particular addresses which are intended for them, while all other addresses are ignored. This is the job of the address decoding circuitry, and that establishes the memory map of the system. As a result, system's memory map may look like in the table ...
When writing to memory, the CPU writes data from MDR to the memory location whose address is stored in MAR. MAR, which is found inside the CPU, goes either to the RAM (random-access memory) or cache. The MAR register is half of a minimal interface between a microprogram and computer storage; the other half is a MDR.
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APB is designed for low bandwidth control accesses, for example register interfaces on system peripherals. This bus has an address and data phase similar to AHB, but a much reduced, low complexity signal list (for example no bursts). Furthermore, it is an interface designed for a low frequency system with a low bit width (32 bits).