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:

Their distinguishing characteristic, however, is that they also have special hardware-related functions beyond those of ordinary memory. So, depending on your 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.

Signals from a state machine to the register control when registers transmit to or accept information from other registers.

Sometimes the state machine routes information from one register through a functional transform, such as an adder unit, and then to another register that stores the results.

Typical uses of hardware registers include:

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.

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