A pair of signals Request (R) and Acknowledge (A) is used to coordinate transactions between a CPU and its I/O system. The interaction of these signals is often referred to as a “handshake.” These signals are synchronous with the clock and, for a transaction, are to have their transitions always appear in the order shown in Figure 4-53. A handshake checker is to be designed that will verify the transition order. The checker has inputs, R and A, asynchronous reset signal, RESET, and output, Error (E). If the transitions in a handshake are in order, E = 0. If the transitions are out of order, then E becomes 1 and remains at 1 until the asynchronous reset signal (RESET = 1) is applied to the CPU.

Figure 4-53:

(a) Find the state diagram for the handshake checker.

(b) Find the state table for the handshake checker.

Transcribed Image Text:

CLK R A E