State Name

State box

Algorithmic State MachineFrom Wikipedia, the free encyclopedia

The Algorithmic State Machine (ASM) method is a method for designing finite state machines. It is used torepresent diagrams of digital integrated circuits. The ASM diagram is like a state diagram but less formal andthus easier to understand. An ASM chart is a method of describing the sequential operations of a digital system.

Contents

1 ASM Method2 ASM Chart3 Datapath4 Detailed ASM Chart5 See also6 References7 External links

ASM Method

The ASM method is composed of the following steps:

1. Create an algorithm, using pseudocode, to describe the desired operation of the device.2. Convert the pseudocode into an ASM chart.3. Design the datapath based on the ASM chart.4. Create a detailed ASM chart based on the datapath.5. Design the control logic based on the detailed ASM chart.

ASM Chart

An ASM chart consists of an interconnection of four types of basic elements: state names, states, conditioncheques, and conditional outputs. An ASM state, represented as a rectangle, corresponds to one state of aregular state diagram or finite state machine.The Moore type outputs are listed inside the box.

State name: The name of the state is indicated inside the circle and the circle is placed inthe top left corner or the name is placed without the circle.

State box : The output of the state is indicated inside the rectanglebox

Decision box: A diamond indicates that the stated conditionexpression is to be tested and the exit path is to be chosenaccordingly. The condition expression contains one or more inputsto the FSM. An ASM condition check, indicated by a diamond with one input and twooutputs (for true and false), is used to conditionally transfer between two states orbetween a state and a conditional output. The decision box contains the stated conditionexpression to be tested, the expression contains one or more inputs of the FSM.

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Decision box Conditional

output box

Conditional output box: An oval denotes theoutput signals that are of Mealy type. Theseoutputs depend not only on the state but also theinputs to the FSM.

Datapath

Once the desired operation of a circuit has beendescribed using RTL operations, the datapathcomponents may be derived. Every unique

variable that is assigned a value in the RTL program can be implemented as a register.Depending on the functional operation performed when assigning a value to a variable, the register for thatvariable may be implemented as a straightforward register, a shift register, a counter, or a register preceded by acombinational logic block. The combinational logic block associated with a register may implement an adder,subtracter, multiplexer, or some other type of combinational logic function.

Detailed ASM Chart

Once the datapath is designed, the ASM chart is converted to a detailed ASM chart. The RTL notation isreplaced by signals defined in the datapath.

See also

FlowchartMealy machineMoore machine

References

Sunggu Lee: Computer Design: An Example of Advanced Digital Logic Design, Prentice-Hall 2000, ISBN0-13-040267-2.Sunggu Lee: Advanced Digital Logic Design: Using VHDL, State Machines, and Synthesis for FPGAs,Thomson 2006, ISBN 0-534-46602-8.Stephen Brown, Zvonko Vranesic: Fundamentals of Digital Logic with VHDL Design.

2nd, McGraw Hill 2004; ISBN 978-0-07-249938-4.3rd, McGraw Hill 2009; ISBN 978-0-07-352953-0.

External links

Background of the Algorithmic State Machine (ASM) Notation (http://www.cse.sc.edu/~jimdavis/Tools/kbs_flowhdl_ASM.htm)Brief Introduction to ASM Charts (http://uhaweb.hartford.edu/jmhill/suppnotes/AsmChart/index.htm)

ASM++: a modern Algorithmic State Machine methodology for RTL designs(http://www.epyme.uva.es/asm++)

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