- Data Register
- Control Register (controls all actions of the device)
- Status Register (reflects the flags for the status of the device at an instant and changes after performing the actions as per device drivers)
2. A device initializes by setting the control register bit and the device closes by resetting the control register bits.
3. Both the status and control register bits will be in the same address space,as the processor reads the status from this address during read operation and writes during the write operation.
4. ISRs can be called either by setting the status flag or a hardware call by a signal to initiate.