In the discussion of Example 9.6, we mentioned a possible use of the mutual exclusion element (ME) to prevent both request inputs to the FSM being equal to 1 at the same time. Design an arbiter circuit for this case.

Example 9.6

A SIMPLE ARBITER In computer systems it is often useful to have some resource shared Example 9.6  by a number of different devices. Usually, the resource can be used by only one device at a time. When various devices need to use the resource, they have to request to do so. These requests are handled by an arbiter circuit. When there are two or more outstanding requests, the arbiter may use some priority scheme to choose one of them, as already discussed in Section 6.8.

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Arbiter Request (r) Grant (g) Request1 Grantl Request2 Grant2 Device 1 Device 2 (a) Arbitration structure (b) Handshake signaling Shared resource