Counters are sequential circuits that employ a cascade of flip-flops that are used to pratyangira devi 1008 names pdf something. We will write the VHDL code for all the three types of synchronous counters: up, down, and up-down.
First, we will take a look at their logic circuits. Then we will write the VHDL code, then test the code using testbenches. Finally, we will synthesize the RTL schematic and the simulation waveforms. Synchronous means to be driven by the same clock. The flip-flops in the synchronous counters are all driven by a single clock input.
You can see the logic circuit of the 4-bit synchronous up-counter above. And four outputs since its a 4-bit counter. And in that case, it is also an input. Since we are using behavioral architecture, we will define the behavior of the circuit using if-elsif statements. The process statement has the inputs in its sensitivity list.
The main program is very simple and straightforward. We will use the infinite testbench type of testbench as we had discussed in our guide on writing a VHDL testbench. After coding the up-counter, we will implement the VHDL code for synchronous down counter using behavioral architecture. First, will understand its behavior.
And then we will understand the syntax. For the full code, scroll down. The 4-bit synchronous down counter counts in decrements of 1. The maximum count that it can countdown from is 16 i.As I understand, the key lines of a VHDL component that describes a two-flip-flop 2FF synchronizer could be the following where siga is being crossed from the clka-domain into the clkb-domain as sigb :. I am asking because in Vivado v If possible as in not illegal due to control sets they will be placed in the same slice.
However, in Vivado v No worries, probably time for me to upgrade my Vivado anyway. One more question please. Please further explain AR and comment on my confusion. I also observe in v These constraints looks like the following:. My 'answer' was to instantiate the iserdes block That AR is a rather awful excuse for why the attribute doesn't work.VHDL Basic Tutorial On Multiplexers(Mux) Using Case Statement
The attribute " can only be applied on cells "? What is this ? We're designing RTL here, folks. Not schematic capture, instatiating primitives. The XDC workaround is klunky - to difficult to manage and insure the attribute gets applied everywhere. I suppose with a scoped XDC I might be able to get things to work, but the attribute was the best solution. Xilinx should fix this. Apparently and I am not a VHDL expert you cannot set a property on a primitive that is instantiated in a generate loop.
The attribute was not being applied to the instantiated cells themselves which can't be done in a generate loop. It is clearly also not being applied to a signal that infers the flip-flops, since they aren't inferring flip-flops, they are directly instantiating the FDRE.
So, the AR is saying that for this particular coding stylethe only option is to do it in Tcl. But if you are inferring flip-flops which is probably the more common casethis AR doesn't apply. Thanks for clarifying the AR.A multiplexer is a device that selects one output from multiple inputs. It is also known as a data selector. Multiplexers are used in communication systems to increase the amount of data that can be sent over a network within a certain amount of time and bandwidth.
The multiplexer MUX functions as a multi-input and single-output switch. The selection of the input is done using select lines. You can find the detailed working and schematic representation of a multiplexer here. Well, in Verilog hardware descriptive language, we have four main abstraction layers or modeling styles. Now before jumping to the coding section, a brief description of each modeling style has been presented before you.
As the name suggests, this style of modeling will include primitive gates that are predefined in Verilog. The prerequisite for this style is knowing the basic logic diagram of the digital circuit that you wish to code. The input signals are D0 and D1. S is the select line with Y as its output. We can orally solve for the expression of the output that comes out to be:.
For the gate level, we will first declare the module for 2: 1 MUX, followed by the input-output signals. The order of mentioning output and input variables is crucial here, the output variable is written first in the bracket, then the input ones. The module is a keyword here. Y is the output and D0D1 and S being input are written after. Next comes the declaration of input, output, and intermediate signals.
You might have noticed that other modeling styles include the declaration of variables along-with their respective data- types. Next comes the instantiation part for gates.
For example for not gate, Sbar is the output and S is the input. This is the design abstraction, which shows the internal circuitry involved. It is the hardware implementation of a system. The dataflow level shows the nature of the flow of data in continuous assignment statements assign keyword.
It describes the combinational circuit by their functions rather than their gate structures. For coding in the dataflow style, we only need to know about the logical expression of the circuit. To start with this, first, you need to declare the module. Now since this the dataflow style, one is supposed to use assign statements.
I have used a ternary operator for the output Y.
This operator? The hardware schematic for a multiplexer in dataflow level modeling is shown below. You will notice that this schematic is different from that of the gate-level. It involves the symbol of a multiplexer rather than showing up the logic gates involved, unlike gate-level modeling.
Tutorial 4: Multiplexers in VHDL
This level describes the behavior of a digital system. In most of the cases, we code the behavioral model using the truth table of the circuit. Now to find the expression, we will use K- map for final output Y. Since it is the behavioral modeling, we will declare the output Y as reg while the rest of the inputs as wire.The Case-When statement will cause the program to take one out of multiple different paths, depending on the value of a signal, variable, or expression.
Other programming languages have similar constructs, using keywords such as a switchcaseor select. Continue reading, or watch the video to find out how! The Case statement may contain multiple when choices, but only one choice will be selected.
And most importantly, the others choice. The waveform window in ModelSim after we pressed run, and zoomed in on the timeline:. Tested on Windows and Linux Loading Gif.
First, we created a process using If-Then-Elsif-Else that would forward one of the signals Sig1Sig2Sig3or Sig4based on the value of the selector signal Sel. Then we created a process that did exactly the same, using the Case-When statement. We can see from the waveform that the output signals from the two processes, Output1 and Output2behave exactly the same.
In our example, the Sel signal has only four legal values. But if there had been a higher number of possibilities, we can easily see that the Case-When statement can help making code more readable. This is the preferred way of creating such a component by most VHDL designers. Understanding of the multiplexer was the bonus point of this exercise.
It is simply a switch that selects one of several inputs, and forwards it to the output. This is an illustration of how our MUX forwards the selected input signal:. We used the others clause to catch all values of Sel which were not ones or zeros.
This indicates an unknown value on this signal, and it will be visible in downstream logic as well. We can see from the waveform that when the Sel signal turned red, Output1 and Output2 also changed to "XX".
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I will test more cases with the TestBench and write here the results, thanks again to everyone for the help :. Latches may be generated from incomplete case or if statements.
VHDL code for D Flip Flop
I'm stuck on the design of a mux and a demux parametrized both in data size and number of ports. Learn more. Asked 4 years, 6 months ago. Active 4 years, 6 months ago. Viewed 5k times. I have in mind something like this : use IEEE. Joe Vinella. Joe Vinella Joe Vinella 23 1 1 silver badge 5 5 bronze badges.
Active Oldest Votes. Using VHDL it can be done like: library ieee; use ieee. Usage example of the mux can be: library ieee; use ieee. Morten Zilmer Morten Zilmer 14k 2 2 gold badges 22 22 silver badges 43 43 bronze badges. Thanks for the MUXit works fine and is a very short and clear code. I have problems with the DEMUX now, using the same constructs leads to warnings of "latches", i edited my question to explain this.
Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a 4 bit counter made of D flip flops and multiplexers. It counts up to and then down to My design is structural. Though i do not know how to make the enable and the load synchronous. Here is my try :. Is this some academic homework or something like that? If not, throw away all those flipflop instances and muxes and just write one clocked procedure.
Something along the line of:. The idea here is to demonstrate how to use bit-wide four input multiplexers although there are some things we can describe based on the counter value as a whole. As chip designers we used to remember this stuff in an earlier era. You paid for a license to use arithmetic elements e. A sort of "You have '0's? Way back when we used to lie '1's on their side" sort of recollection.
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In any event you tend to remember the short cuts, increment and decrement with '0' values for the B input of an adder drops the one XOR and requires the not values. The four inputs to the multiplexers require two select inputs.
You can arbitrarily assign function to inputs and select values. For example:. Where load takes precedence over counting. The sel inputs are used to all four multiplexer. Note that equations for "10" and "11" values of sel are combined on the following code's MUX0, you can use a 4 input multiplexer and supply not q 0 to both inputs:. The other thing of note is that there's an added input port to supply the load value, arbitrarily named counterin to match counterout.
So here's one way to organize the four input muxes to provide hold no increment, no decrement, no loadload, increment and decrement. You could also note it anticipates an asynchronous reset. Learn more. Counter 4bit with synchronous load and enable and asynchronous reset. Ask Question. Asked 4 years, 4 months ago. Active 4 years, 4 months ago. Viewed 3k times. Katerina Tsellou Katerina Tsellou 65 1 1 silver badge 10 10 bronze badges. What's the question?
What have you tried? Also i want to make my load and enable synchronous and i do not know how.Post a Comment. Verilog code for D Flip Flop here. Simulation waveform for D Flip-Flop:. Recommended VHDL projects : 1. What is an FPGA?
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Newer Post Older Post Home. Subscribe to: Post Comments Atom. Today, f Verilog code for counter with testbench. In this project, Verilog code for counters with testbench will be presented including up counter, down counter, up-down counter, and r Verilog code for D Flip Flop.
D Flip-Flop is a fundamental component in digital logic circuits. Verilog code for D Flip Flop is presented in this project. There are tw This FPGA project is aimed to show in details how to process an image using Verilog from reading an input bitmap image. Verilog code for FIFO memory. The RISC processor is designed based on its instructi This Verilog project provides full Verilog code for the Clock Divider on There are several types of D Flip Flops such A display controller will be