A disadvantage of conditional programmed I/O is that the microcomputer needs to check the status bit by waiting in a loop. This type of I/O transfer is dependent on the speed of the external device. For a slow device, this waiting may slow down the capability of the microprocessor to process other data. the polled I/O and interrupt I/O techniques are efficient in this type of situation. The external device is connected to a pin called the interrupt (INT) pin on the microprocessor chip. The microcomputer then automatically loads an address into the program counter to branch to a subroutine-like program called the interrupt service routine. This program is written by the user. The external device wants the microcomputer to execute this program to transfer data. the last instruction of the service routine is a RETURN.
No comments:
Post a Comment