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:^{[citation needed]}

• 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.^[citation needed]

Hardware registers are used in the

. 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

.

Functionality

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.^[1]

Reading a hardware register in "peripheral units" —

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 verification

, testing and documentation.

Registers can be read/write, read-only or write-only.

Register varieties

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The hardware registers inside a central processing unit (CPU) are called processor registers.

Strobe registers have the same interface as normal hardware registers, but instead of storing data, they trigger an action each time they are written to (or, in rare cases, read from). They are a means of

.

Registers are normally measured by the number of bits they can hold, for example, an "

register".

Designers can implement registers in a wide variety of ways, including:

• register files
• standard SRAM
• individual flip-flops
• high-speed
  core memory

In addition to the "programmer-visible" registers that can be read and written with software, many chips have

.

Standards

SPIRIT IP-XACT and DITA SIDSC XML define standard XML formats for memory-mapped registers.^[4][5][6]

See also

• Processor register
• Register-transfer level (RTL)

References