There are several ways of combining with interrupt I/O, some involving only software, some only hardware, and some a combination of the two. Let us consider the following means of giving priority to an interrupt system:

1. Polling
2. Daisy chaining
3. Interrupt priority management hardware

By putting a program sequence (similar to the one in Fig.6-7) at the beginning of the interrupt routine, the priority of the interfaces could be established by the order in which they are polled by the sequence.

Daisy chaining is a simple hardware means of attaining a priority scheme. It consists of associating a logic circuit with each interface and passing the interrupt acknowledge signal through these circuits as shown in Fig.6-14(a). The details of a daisy chain logic are shown in Fig.6-14(b). The priority of an interface is determined by its position on the daisy chain. The closer it is to the CPU the higher its priority.