Polls

When a processor wants to access the device, one approach is to let processor does all the work. The processor interacts with the controller through an elaborate protocol, but the basic handshaking is quite simple, namely:
1. CPU continuously reads the status bits until the bits that indicates the device is ready to receive commands the CPU.

2. CPU-write enable bit in a register command as the initial sign of the CPU gives a command and writes a byte in the data-out.

3. CPU activates the command-ready bit, meaning that the command is available to run the controller.

4. The controller saw the command ready bits are set so that bit of work on-set.

5. The controller reads the command registers and see the command write the data read-out and
ordered the I / O CPU to do what was ordered.

6. Controller erase command ready bits, bit and bit errors in the status of work.
Step 1 is called polling or busy waiting. Processor continuously reads the status bit, hoping a bit that indicates when the device is ready to receive his orders. Basically polling can said to be efficient when the performance of the device and its controller quickly. The weakness of this method is if the long waiting time, then it is better that the other processor tasks. As for knowing whether the device is ready to take orders again or not, is used
interruptions.