A read-only register is a special type of register that can only be read by the programmer. Read-only registers are typically used for things such as status registers, certain control registers, hardware timers, counters, and data buses where data is only transmitted. Attempting to write to such registers typically results in a NOOP or an exception, or on some older systems a crash. On various microprocessors some read-only registers can sometimes be set at boot time.

See also

• write-only register