Interrupt-driven data transfer in 8085


We use this method when there is a lack of accurate knowledge of the timing characteristics of the Input Output device which takes maximum time for the device to be ready for use. Suppose we resort for the checking of data transfer; the processor here wastes a huge time in the loop for the device to get ready up to the mark. For avoiding this problem, we use the interrupt-driven data transfer process. Here the processor goes ahead with its desired work, and as soon as the device is ready for data transfer process, the corresponding Input Output port sends a signal for interrupt request to the processor. The arrival of the interrupt request be the half way throughout the execution of the instruction. After that the entire set of instruction is completed.

This is a very complex method. But the advantage is that the processor employed here does not wastes its time for the loop checking as well as the device to get ready for use. An example to be cited as if 8085 is allowed for reading from the keyboard, the one way is just to continuously scan the keyboard by looking at the key which is pressed. This method is called the status check method. It happens as such in one second when the key is already pressed. For this amount of time 8085 is in a loop for this amount of time waiting for the depression of the key. In this span of time, the 8085 should have executed about 500,000 instructions, assuming an average time of execution of 2 μs for each instruction! In the interrupt-driven data transfer scheme, the 8085 executes about 500,000 useful instructions, by the time at which a key is pressed at the keyboard by the user. This results sending of an interrupt signal to the 8085 by the Input Output port.

Published on 12-Mar-2019 17:03:01