Hardware register

In digital electronics, especially computing, hardware registers are circuits typically composed of flip flops, often with many characteristics similar to memory, such as: The ability to read or write multiple bits at a time, and Using an address to select a particular register in a manner similar to a memory address. Their distinguishing characteristic, however, is that they also have special hardware-related functions beyond those of ordinary memory. So, depending on the point of view, hardware registers are like memory with additional hardware-related functions; or, memory circuits are like hardware registers that just store data. Hardware registers are used in the interface between software and peripherals. Software writes them to send information to the device, and reads them to get information from the device. Some hardware devices also include registers that are not visible to software, for their internal use. Depending on their complexity, modern hardware devices can have many registers. Standard integrated circuits typically document their externally-exposed registers as part of their electronic component datasheet. Typical uses of hardware registers include: configuration and start-up of certain features, especially during initialization buffer storage e.g. video memory for graphics cards input/output (I/O) of different kinds status reporting such as whether a certain event has occurred in the hardware unit, for example a modem status register or a line status register. Reading a hardware register in "peripheral units" — computer hardware outside the CPU — involves accessing its memory-mapped I/O address or port-mapped I/O address with a "load" or "store" instruction, issued by the processor. Hardware registers are addressed in words, but sometimes only use a few bits of the word read in to, or written out to the register. Commercial design tools simplify and automate memory-mapped register specification and code generation for hardware, firmware, hardware verification, testing and documentation.