Full VHDL code for Moore FSM Sequence Detector - m-jahn.info
VHDL 6. examples of FSM ver.8a. Counters and pattern generators. Up/down Date: . Change FSM coding styles in Xilinx-ISE. In Implementation view, right. We generate VHDL code corresponding to Moore Finite State Machine (FSM), because is similar with the logic Date Added to IEEE Xplore: 26 January If you represent your FSM with a diagram like the one presented in Figure 3 or Figure 4, the VHDL FSM coding is straightforward and can be.
They should also have a basic understanding of VHDL or at least have some experience reading structured computer code. Experience with computer code will help you recognize some of the structures and constructs of VHDL, but it should be noted that VHDL is not a programming language; it is a hardware description language HDL.
In other words, the statements that you write are going to create hardware gates, flip flops etc. This FSM has four states: A, B, C, and D. The system has one input signal called P, and the value of P determines what state the system moves to next.
If P is low, and the system is in state A, B, or C, the state is not changed. The system also has an output called R which is 1 if in state D, otherwise it is a 0. Figure 1 is the diagram for the FSM, but first here are a few notes about this diagram: The circles represent the states Arrows between the circles represent the rules for changing from state to state. The arrow coming from "nowhere" to the A indicates that A is the initial state. It is important to remember that when writing the VHDL code, what you are doing is describing how you want the hardware i.
How to Implement a Finite State Machine in VHDL
So, for example, when you define a set of states like A, B, C, and D in this system, those states are going to be represented by bits, and more specifically by the output of flip flops. There are other ways that the states could be represented too. One of those ways would be to use four bits, where each bit represents a state, but only one bit can be on at a time.
So A would be represented byB byC by and D by One of the good things about using a high level hardware description language is that you can often ignore this level of detail. Figure 2 shows the general idea of the hardware circuitry that will be created when the VHDL code is synthesized to create the hardware. Block Diagram Representation of Logic Created for a State Machine This diagram indicates that there is a set of n flip flops that represent the state.
Implementing a Finite State Machine in VHDL
There is also some logic that uses the output of the flip flops and the inputs to the system to determine the next state. Finally, there is some logic that decodes the output values of the flip flops to create the m output signals.
Again, when using a HDL, you can often ignore this level of detail in your design. It is still important to understand what kind of circuitry is created by your HDL because there may come a time when you have to count and minimize the number logic gates in your design.
With an understanding of what is created by your HDL statements you can then design to minimize gate creation. The VHDL entity describes the external interface of the system you are designing which includes the inputs, the outputs, and the name of the entity.
Full VHDL code for Moore FSM Sequence Detector
The general form of an entity looks like this: The name of the entity will be SimpleFSM, the inputs are a clock signal, the reset signal and the P signal, and the output is the R signal. It should be mentioned that the clock signal is the periodic high-low signal that controls the timing to this synchronous system. Any synchronous system has one controlling clock signal that synchronizes all of the blocks in the system making them change at the same time.
Putting all of the information together gives a SimpleFSM entity that looks like this: The next step is to define the functionality of the entity; this block of VHDL is called the architecture. The functionality that we are implementing is that of the state machine defined in figure 1.
The example below shows the code that would be needed to implement the SimpleFSM. While this code is specific to the SimpleFSM, I will describe what each of the sections of the code do so that it will be an easy process to replace this code with code for your own state machine. The architecture definition states: RTL, which stands for register-transfer level, is a mid-level of abstraction. Sometimes behavioural descriptions are too high level and cannot actually be synthesized into hardware. The fundamental difference between these two types lies in the management of the outputs: The output of the Mealy FSM depends on the present state and inputs.
Designated Numbers Moore FSM with 4 bit counter - FPGA - Digilent Forum
The outputs of a Moore machine depend only on the present state and not on the inputs. No assumptions or check on the inputs have to be performed to generate the output of the FSM, so the output decoding is simpler to handle. Moreover, if the output is combinatorial, i.
The transition from one state to another state is represented by the connection arrows. In order to move from a current state to the next one the condition, on the connection arrow, shall be verified. If no condition is present on the connection arrow the next state will be the current state after a clock cycle. Clocked Process for driving the present state; Combinatorial Process for the next state decoding starting from the present state and the inputs; Clocked or combinatorial Process driving the FSM output.
Note that the present state is stored in registers while the next state is completely combinatorial. The advice is to register all the FSM outputs unless it is absolutely necessary to recover a clock cycle, I mean you have to provide the FSM output with the lowest possible clock latency. Using registered outputs, you will improve the system timing performances. A good example is far better than a good precept.
Suppose we want to implement an automatic vending machine.