Nidal Feedback Privacy Policy Feedback. To make this website work, we log user data and share it with processors. Various enhancements mxchine to the von Neumann architecture exist which compensate for the bottleneck, pipelining and cache memories are probably examples you are familiar with, and alternative architectures exist too. It is our basic tool for organizing our thoughts, and we use it to guide the design process. Output depends on inputs and memory:. There was a problem providing the content you requested Click here to sign up.

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You are on page 1of 29 Search inside document Dr. Narasimha Murthy. D yayavaram yahoo. These names are often used when the sequential circuit is used to control a digital system that carries out a step-by-step procedure or algorithm. The state graphs are used to define state machines for controlling digitial circuits like adders, multipliers, and dividers.

As an alternative to using state graphs, a special type of flowchart, called a State Machine flowchart or SM Chart, is also widely used to describe the behavior of a state machine. Flowcharts are useful in software design, similarly SM Charts are useful in the state machine hardware design of digital systems. This is a also special type of a flow chart flowchart, or SM chart for short. SM charts are also called ASM algorithmic state machine charts. These SM Charts have many advantages.

It is often easier to understand the operation of a digital system by inspection of the SM chart instead of the equivalent state graph. A given SM chart can be converted into several equivalent forms, and each form leads directly to a hardware realization.

SM Charts : A State Machine chart which is similar to a flow-chart is used to describe the behavior of a digital system or state machine. The ASM chart has many advantages over state graphs. It is also easy to understand the operation of a digital system by the inspection of the SM Chart rather than the state graph.

The basic difference between an ordinary flow chart and SM chart is that ,certain specific rules must be followed to constructing the SM chart ,but no such specific rules are to be followed in the case of flow-chart. There are three important components in an SM Chart. After the state assignment ,a state code must be placed outside the box at the top. Decision Box: A decision box is represented by the diamond shape symbol with true and False branches.

The condition placed in the box is a Boolean expression that is evaluated to determine which branch is true. State box b. Decision box c. Conditional Output box Conditional output Box: The conditional output box , which has curved ends contains a conditional output list.

The conditional outputs depend on both the state of the system and inputs. For every valid combination of input variables ,there must be exactly one exit path defined. This is necessary because ,each allowable input combination must lead to a single next state.

The second rule is no internal feedback within an SM block is allowed. This is shown in the diagram below. Here Za,Zb and Zc are the Moore outputs. And Z1 ,Z2 are the Mealy outputs which change after a state change or input change. The Moore outputs change only after a state change. The equivalent state chart is shown below. Next ,the required input,output signals must be defined. Then the SM Chart must be constructed ,that tests the input signals and generates the proper sequence of the output signals.

Let us consider the case of a binary Multiplier. In the binary Multiplier ,there will be a add shift controller which generates required sequence of add and shift signals.

In S1,the Multiplier bit M is tested. In S2, a shift signal is generated ,since a shift must always follow and add. In S3 ,the Done signal is turned ON. Dice Game: Let us derive the SM chart for the electronic dice game. Figure below shows the block diagram for the dice game.

Here two counters are used to simulate the roll of the dice. Each counter Dr. Thus, after the roll of the dice, the sum of the values in the two counters will be in the range 2 through The two important rules of the game are as follows: 1. After the first roll of the dice, the player wins if the sum is 7 or He loses if the sum is 2, 3, or Otherwise, the sum which he obtained on the first roll is referred to as his point, and he must roll the dice again.

On the second or subsequent roll of the dice, he wins if the sum equals his point, and he loses if the sum is 7. Otherwise, he must roll again until he finally wins or loses. The inputs to the dice game come from two push buttons, Rb roll button and Reset. Reset is used to initiate a new game. When the roll button is pushed, the dice counters count at a high speed, so the values cannot be read on the display. When the roll button is released, the values in the two counters are displayed and the game can proceed.

Because the button is released at a random time, this simulates a random roll of the dice. If the Win light or Lose light is not on, the player must push the roll button again.

The components for the dice game shown in the block diagram include an adder which adds the two counter outputs, a register to store the point, test logic to determine conditions for win or lose, and a control circuit. The input signals to the control circuit are defined as follows: Dr. If the sum is 7 or 11, the circuit goes to state S2 and turns on the Win light; otherwise, D is tested.

If the sum is 2, 3, or 12, it goes to state S3 and turns on the Lose light; otherwise, the signal Sp becomes 1, and the sum is stored in the point register.

It then enters S4 and waits for the player to roll the dice again. Otherwise, the control returns to S4 so that the player can roll again. The realization consists of a combinational sub network ,together with flip-flops for storing the states of the network. Sometimes it is possible to identify equivalent states in an SM chart and eliminate redundant states.

However, in an SM chart all inputs are not tested in every state, as it makes makes the reduction procedure more difficult. Even if the number of states in an SM chart can be reduced, it is not always desirable to do so because combining states may make the SM chart more difficult to interpret. Before deriving next-state and output equations from an SM chart, a state assignment must be made. The best way of making the assignment depends on how the SM chart is realized.

If gates and flip-flops or the equivalent PLD realization are used, the guideline method of state assignment is more useful. The SM chart of the Multiplier is shown below. The PLA has five inputs and six outputs.

Here binary assignment is made for states. Because S0 has two exit paths, the table has two rows for present state S0. Because only St is tested in S0, M and K are dont-cares as indicated by dashes. The outputs for each row can be filled in by tracing the corresponding link paths on the SM chart. The PLA has nine inputs and seven outputs. Because state has four exit paths, the PLA table has four corresponding rows.

When Rb is 1, Roll is 1 and there is no state change. For the link path from state to , Rb, D, and D are all 0, and Sp is a conditional output. In state , the Win signal is always on, and the next state is or , depending on the Dr. Similarly, Lose is always on in state States and are unused, so all inputs and outputs are dont-cares in these states.

This makes the problem more complicated. In such situations certain alternate methods are used where the use of MUX s is considered. In such methods ,the inputs to the PLA are taken from the state register. The PLA output has four fields. In each state. If the input is 1 i. The out-put field is the same as for standard realization. But this SM chart has only Moore outputs. The PLA table is derived using binary state assignment. To test these variables an 8 to 1 MUX is used as shown below.

The MUX is used to implement the block diagram shown above. The same block diagram can be modified by replacing the state register with a counter as shown below. The TEST field selects one of the inputs to be tested in each state. If the selected input is true 1 the NST field is loaded into the counter. If the selected input is 0 ,the counter is incremented. For each condition box ,for the false branch, the next state is assigned in sequence if possible. If this not possible extra states called X-states must be added.



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