Chapter D Finite State Machines

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Converting the numerical values of the states in the above table to bits, we obtain theisomorphic table, shown in Fig.24(a). A ROM-based implementation is shown inFig.24(b).Line This IpL ipR Next L R F B12300 0 0 00 0 0 1 000 0 1 00 0 0 1 000 1 0 01 0 0 1 04 00 1 1 00 0 0 1 05 01 0 0 00 0 1 0 06 01 0 1 00 0 1 0 07 01 1 0 01 0 1 0 08 01 1 1 00 0 1 0 0S(a)addr0000100000 0000100001 0100100010 0000100011 0001000100 0001000101 0101000110 0001000111ROMLR(b)clkFigure 24. Robot Controller shows as (a) the Encoded <strong>State</strong> Transition Table for therobot controller ROM contents generated by encoding state “Q0” as 00 and state “Q1”as 01. (b) with the ROM contents used to implement this controller
D.18 Moore and Mealy <strong>Machines</strong>You may have noticed that a FSM involves a number operations. First the presentstate is combined with the stimulus input. Second an output is produced. Third, thestate is updated, i.e., there is a transition. It turns out that there are two differentarchitectures for combining thes e operations. These are known a s “Moore” and“Mealy” architectures. Our discussion has been centered around the “Moore”machine where the output is generated by the present state. In other words the outputis associated with the state. The transition serves to move between states dependingon the input stimulus. The transition was always associated with a clock signal. Butwe can do this another way. We can associate the output with the transition betweenstates. So, as soon as a stimulus is received, it produces a new output, without havingto wait for the clock signal. This is the “Mealy” architecture, where the clock signal isused to move between states, but not generate the output. So in the Moorearchitecture, the output as well as generation of the new state happens on the clocksignal, even though the stimulus may have arrived some time before the clock signalis issued. In the Mealy architecture, as soon as the stimulus is received, the outputresponse obtains, the stimulus “flows through” to the output.Input S/CICOPSNS/L/ /Output R/clk(a)Input SPS/ // Output RCI/L/CO/clk(b)Figure 25. Two architectures of FSMs. (a) the “Moore” machine we have beendiscussing in this chapter. Here the output is only a function on the present state PS,while in (b) the “Mealy” machine, the output R depends on the PS and also the inputstate S. The output of the Mealy machine changes during the transition from the PS tothe NS and not when the PS is established.
Page 7 and 8: D4. A Parity CheckerOur second exam
Page 9 and 10: Now for the transitions between the
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Page 13 and 14: A Similar chain of events leads us
Page 15 and 16: D11. Designing a Soft-Drink Dispens
Page 17 and 18: output (R) from the present state.
Page 19 and 20: That’s the job of the CO block wh
Page 21 and 22: two tables, one which shows the two
Page 23 and 24: Keypadinput SPS2PS1/1CINS2NS1/2LCO/
Page 25 and 26: (a)Saddr000000010010001101000101011
Page 27: Line This IpL ipR Next L R F B1 Q0
Page 31 and 32: Another suggestion has been made by
Page 33 and 34: Question.3 Design a FSM which will
Page 35 and 36: The following activities lead you t
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Chapter D Finite State Machines

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