Jan 20, 2019 · Microprocessors and Embedded Systems | Address Bus Data Bus Memory Size
Aug 04, 2008 · The address bus transports memory addresses which the processor wants to access in order to read or write data. It is a unidirectional bus. The data bus transfers instructions coming from or going to the processor.
Jul 19, 2000 · If you've got a 16-bit address bus (so 65536 possible address) and a 16-bit data bus, you can still address 65536 different physical memory locations, but each one is a 16-bit value. As a 16-bit value can also be considered as two 8-bit bytes, you can address 128k(bytes) of actual memory with this setup) In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into three subassemblies. The first is the address bus (sometimes called the memory bus), which transports memory addresses that the processor wants to access in order to read or write data. It is a unidirectional bus. Address Bus ze.g. CPU needs to read an instruction (data) from a given location in memory zIdentify the source or destination of data zBus width determines maximum memory capacity of system – e.g. 8080 has 16 bit address bus giving 64k address space Address Bus Size Addressable memory (bytes) 12 24 38 416 532 664 7128 8256 9512 10 1K 11 2K 12 ... m Bits in a logical memory address 20 bits20 bits 32 bits s Bits in smallest addressable unit 8 8 8 b Data Bus size 8 16 64 2m Memory wd capacity, s-sized wds 220 220 232 2mxs Memory bit capacity 220x8 220x8 232x8 "address" yes. "bus" no. 32-bit/64-bit refers to the size of an address as used by all native software. A "bus" has to be a physical address (but a physical address doesn't need to be a "bus"). The physical address for any one model of 32 bit x86 chip may be larger or smaller than 32 bits. The data bus is the bus which is primarily responsible for transferring data between the CPU, memory and the motherboard. The word addressable size of the computer refers to the size of a single unit of data that can be transferred, so knowing that gives you the width of the data bus.
You can use GPIOs to emulate additional address bits. In this case you have to set the GPIO before you can access a certain memory area. Or you can decode the multiplexed data/address bus by yourself, instead of using the internal CPLD. In this case you can decode up to 28bits. An address bus is measured by the amount of memory a system can retrieve. A system with a 32-bit address bus can address 4 gibibytes of memory space. Newer computers using a 64-bit address bus with a supporting operating system can address 16 exbibytes of memory locations, which is virtually unlimited. The width of a bus is the number of signal lines that constitute the bus. The figure shows for simplicity three busses for distinct functions. Over the address bus, the µP transmits the address of that I/O device or memory locations which it desires to access.