Implement Program Counter Vhdl Code

A Bit of Background In digital systems, there are two basic types of circuits. The first type are. In combinational logic circuits, the outputs depend solely on the inputs. Examples of combinational logic circuits include adders, encoders, and multiplexers. In adders, for example, the output is simply the sum of the inputs; it doesn't matter what any of the previous inputs or outputs were.

The second type of digital logic circuits are. In sequential logic circuits, the outputs depend not only on the inputs, but also on the present state of system (i.e., the values of the outputs and any internal signals or variables). Sequential logic circuits range in complexity from simple counters that move from one state to another in a basic sequence (e.g., 0,1,2,30,1,2,3) to very large scale circuits such as microprocessors with millions of different states or more.The focus of this article will be on the representation of sequential logic circuits as finite state machines and how to convert those finite state machines into the hardware description language VHDL. Sequential logic systems are (FSMs). As FSMs, they consist of a set of states, some inputs, some outputs, and a set of rules for moving from state to state. When doing digital system design, it is very common to begin by defining how the system works with a finite state machine model.

An up/down counter written in VHDL and implemented on a CPLD. Also demonstrates the VHDL. Tutorial 19: Up/Down Counter in VHDL. Created on: 18 March 2013. VHDL Code for up_dn_counter. The up/down counter is created with the following VHDL code. Implementation of stack in VHDL. --Empty descending stack implementation in VHDL. Sir i need the vhdl codes of remaing stack. Please kindly mail.

This design step allows the designer to think about the design from a high-level point of view without having to think much about what kind of hardware the system will be implemented on or what design tools will be required to implement the design. Once the FSM is fully designed, if it is designed well, it is easy to write out the design in a hardware description language (such as Verilog or VHDL) for implementation on a digital IC (integrated circuit). Download games motogp. This article will go through the design process of creating a digital system by first defining a design problem, second, creating the computational model of the system as a finite state machine and third, translating the FSM into the hardware description language VHDL. (VHDL is actually a double acronym. VHDL stands for VHSIC Hardware Description Language and VHSIC stands for Very High Speed Integrated Circuit). Readers should have some experience with. 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.) in the system you are designing. The Finite State Machine The system to be designed is a very simple one and its purpose is to introduce the idea of converting a FSM into VHDL. 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. The system changes state from A to B to C to D as long as the input P is high (1).

If P is low, and the system is in state A, B, or C, the state is not changed. If the system is in state D, it changes to B if P is high and to A if P is low. 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. For example, in this system, the state machine moves from state A to state B if the input P is equal to 1 (otherwise it remains in state A).

The information underneath the line in the circle represents the output value when in each state. The arrow coming from 'nowhere' to the A indicates that A is the initial state. A Simple Finite State Machine This fully defined state machine can very easily be converted into VHDL.

It is important to remember that when writing the VHDL code, what you are doing is describing how you want the hardware (i.e., the digital gates) implemented. 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. In a system with four states, like this one, it would be possible to represent those four states with 2 bits (2 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 by 0001, B by 0010, C by 0100 and D by 1000. 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.

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. VHDL Implementation of Design The first step in writing the VHDL for this FSM is to define the VHDL entity. 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.

The general form of an entity looks like this: ENTITY -entityName- is PORT (-portName1-: -signalDirection- -type-; -portName2-: -signalDirection- -type-; - -portNamen-: -signalDirection- -type-; END -entityName-; -Note: user defined entries are between the dashes Using this template, the entity for the simple FSM can be created. 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: ENTITY SimpleFSM is PORT (clock: IN STDLOGIC; P: IN STDLOGIC; reset: IN STDLOGIC; R: OUT STDLOGIC); END SimpleFSM; One final note about the entity is that all the inputs and outputs are single bits and so can use the data type stdlogic which is the standard type in VHDL for single bit signals. 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. Architecture definition for the SimpleFSM entity Architecture RTL of SimpleFSM is TYPE Statetype IS (A, B, C, D); - Define the states SIGNAL State: StateType; - Create a signal that uses - the different states BEGIN PROCESS (clock, reset) BEGIN If (reset = ‘1’) THEN - Upon reset, set the state to A State IF P='1' THEN State IF P='1' THEN State IF P='1' THEN State IF P='1' THEN State State IF P='1' THEN State State.

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Library IEEE; use IEEE.STDLOGIC1164.ALL; use IEEE.STDLOGICARITH.ALL; use IEEE.STDLOGICUNSIGNED.ALL; entity CounterVHDL is port( Number: in stdlogicvector(0 to 3); Clock: in stdlogic; Load: in stdlogic; Reset: in stdlogic; Direction: in stdlogic; Output: out stdlogicvector(0 to 3) ); end CounterVHDL; architecture Behavioral of CounterVHDL is signal temp: stdlogicvector(0 to 3); begin process(Clock,Reset) begin if Reset='1' then temp.