Vhdl interview questions vhdl interview questions and answers for freshers and experienced candidates to help you to get ready for job interview, after preparing these vhdl programming questions pdf, you will get placement easily, we recommend you to read vhdl interview questions before facing the real vhdl interview questions freshers experienced. Ciletti, advanced digital design with the verilog hdl, pearson education, inc. Digital design with an introduction to the verilog hdl. You do realize assembly and verilog vhdl have as much in common as setting a train schedule and laying the tracks. Vhdl can also just seem more natural to use at times. Vhdl references ieee standard vhdl language reference manual 1076 1993 10762002 rtl hardware design using vhdl coding for efficiency, portability, and scalability by pong p. If a or b are either x or highz, then the expression evaluates to 0 false. Extensive crossprobing provides support for crossprobing between verification tools and design source files. The difference between these styles is based on the type of concurrent statements used. Verilog has its origins in gate and transistor level simulation for digital electronics logic circuits, and had various behavioral extensions added for verification.
I then invoked iverilog using the following commandline, finding that some errors did occur. Note that the icarus vhdl target was designed for translating synthesizable verilog code. Modules verilog language uses a hierarchical, functional unit based design approach. The verilog language originally a modeling language for a very ef. Looking at this example code, we can compare at the how a mux can be programmed through vhdl and verilog. The most obvious difference is that variables use the. Advancements over the years system design pyramid history. Behavioural verilog code generally looks more like a sequential computer program running from top to bottom within an initial begin block. In fact you have to choose the one you need, but its most likely, that you use both, if you need systemc, while there are enough designs left, which need only vhdl verilog. Introduction to verilog, language constructs and conventions, gate level modeling, behavioral modeling, modeling at data flow level, switch level modeling, system tasks, functions, and compiler directives, sequential circuit description, component test and verifiaction. Microprocessors are usually programmed with c language and fpgas used verilog or vhdl language which is actually converted into logic building blocks on fpga integrated circuit.
Vhdl and verilog both are hardware description language. But when signed and unsigned operands are mixed in an expression, things may become tricky. If youre sloppy with case in the original vhdl, the resulting verilog will have compiletime warnings or errors. Project is to design and implement a hardware that performs two stages of operations on an input array and grnerates output. Its the same language, but different styles are used.
Bringing ultra high productivity to mainstream systems. Difference between casex and casez the case, casex and casez all do bitwise comparisons between the selecting case expression and individual case item statements. The gcd is modeled at the algorithmic level in vhdl, verilog and for comparison purposes, c. Verilog, intended as a simulation language, it much closer to c in style, in that it is terse and elegant to write but requires much more care to avoid nasty bugs.
If you get a vhdl architecture to compile, its probably going to approximate to the function you wanted. Using verilog and vhdl wilson, peter robert this book provides a rich toolbox of design techniques and templates to solve practical, everyday problems using fpgas. A verilog design can instantiate a vhdl component corresponding to a vhdl entity only. Vhdl and verilog are hdl and is used for rtl coding to produce synthesizable digital models.
Jan 25, 2016 vhdl was written as a description language, whereas verilog was written as a hardware modeling language. The code in verilog file is inserted for the next processing phase. Vhdl interview questions freshers experienced vhdl. Write verilog code for half adder and full adder logic circuit. Compared to vhdl, verilog data types are very simple, easy to use and very much geared towards modeling hardware structure as opposed to abstract hardware modeling. To answer your question, you need to understand the difference between how digital circuits work, and how a digital modeling language like verilog, vhdl, or systemverilog hdl works. Both verilogb and vhdl simulators to simulate large digital circuits quickly gained acceptance from designers. Free verilog books download ebooks online textbooks tutorials. Vhdl is the older of the two, and is based on ada and pascal, thus inheriting characteristics from both languages. Free download ebooks actions by nature can result in closed roads and other facilities. Reference guide and the verilog ieee 64 pli quick reference guide. Verilog compared to vhdl, verilog data types a re very simple, easy to use and very much geared towards modeling hardware structure as opposed to abstract hardware modeling.
You can use the sort switch to tell the tool to sort the files before processing them, this sort switch is mandatory if your input files are in random order. A possible answer to an audience about a comparison between the languages can go something like this. For high level behavioral modeling, vhdl is better verilog does not have ability. Verilog supports wire and reg data types while systemverilog supports various data types such as enum, struct, union, class and string. The first major extension was verilog xl, which added a few features and implemented the infamous xl algorithm which was a very efficient method for doing gatelevel simulation. Btw vhdl is imho a bit better on closing the gap between system and asic, but systemverilog. Synthesis provides expanded language support for system verilog and vhdl 2008. I dont often convert vhdl to verilog but when i do it is not the most exciting task in the world that is an understatement. Verilog does have very useful unary reduction operators that are not in vhdl. Digital design with an introduction to the verilog hdl, vhdl, and systemverilog m. Verilog constructs are based approximately 50% on c and 50% on ada. Verilog hdl originated in 1983 at gateway design automation. Vhdl and verilog module1 worcester polytechnic institute. Although there could be wide range of questions and can be asked from any topics,so its always better to grasp all the concepts and also the level of toug.
Suitable to be used for serial execution of instruction. Even though hdls were popular for logic verification, designers had to manually. A behavioral architecture uses only process statements. Microcontroller vs fpgadifference between microcontroller. Unlike vhdl, all data types used in a verilog model are defined by the verilog language. This is a simplified version of convolutional neural network implemented in.
Vhdl verilog and vhdl are equivalent for rtl modeling code that will be synthesized. A model with a signal whose type is one of the net data types has a corresponding electrical wire in the implied modeled circuit. Verilog generally requires less code to do the same thing. Vhdl lends itself to describing hardware at more abstracted levels like case statements, ifthen, etc.
A dataflow architecture uses only concurrent signal assignment statements. Well that is not true, i have a strong preference for myhdl, and an insubstantial preference for vhdl over verilog. If you understand the differences between blocking and nonblocking assignments in terms of simulation, then these rules are selfevident. Chu, wileyinterscience, 2006 introductory vhdl from simulation to synthesis by sudhakar yalamanchilli, 2002, xilinx design series. A vhdl design is allowed to instantiate one or more verilog modules.
When looking at verilog and vhdl code at the same time, the most obvious difference is verilog does not have library management while vhdl does include design libraries on the top of the code. We call it digital circuitry, but really we apply analog voltagescurrents to the inputs of analog devices which in turn control the voltagescurrents of their. Vhdl is a rich and strongly typed language, deterministic and more verbose than verilog. The second part contains a worked example of a model that computes the greatest common divisor gcd of two numbers. To work with negative values, the user has to declare a signed variable explicitly. Can you explain me what is major differences between verilog, systemverilog, verilog 1995 and verilog 2001. For casex and casez, comparisons are performed using the identity operator instead of equality. The complexity of asic and fpga designs has meant an increase in the number of specialist design consultants with specific tools and with their own libraries of macro and mega cells written in either vhdl or verilog. Apr 11, 2016 verilog is not as verbose as vhdl so thats why its more compact. Vhdl or verilog rtl, after exploring a multitude of microarchitectures based on design requirements.
Instantiation of a verilog udp inside a vhdl design is not supported. The implementation was the verilog simulator sold by gateway. Here speed is proportional to execution time of the instruction. The logic function of asic is specified in a similar way as in the case of fpgas, using hardware description languages such as verilog or vhdl. Vhdl may be preferred because it allows a multitude of language or user defined data types to be used. With an introduction to the verilog hdl, vhdl, and systemverilog, 6th edition by m. Real chip design and verification using verilog and vhdl pdf. The whole design consists of several smaller modules the complexity of the modules is decided by the designer verilog module. Vhdl has some features that make it good for systemlevel modeling, whereas verilog is much better than vhdl at gatelevel simulation. Extend verilog ieee 2001 to higher abstraction levels for architectural and algorithmic design, and advanced verification. Difference between verilog and vhdl difference between.
Scripting support supports commandline operation and tcl scripting. Verilog simulator was first used beginning in 1985 and was extended substantially through 1987. What is the difference between verilog and systemverilog. An architecture can be written in one of three basic coding styles. Verilog, being the opposite in terms of its features, looks similar to c code, which is why it is often easier to learn. There are net data types, for example wire, and a register data type called reg. I expect that this is the only book in print with vhdl 93 and verilog 95 examples side by side.
Vhdl has roots in the ada programming language in both concept and syntax, while verilog s roots can be tracked back to an early hdl called hilo and the c programming language. Programmable logic design grzegorz budzy n lecture 12. The main difference between behavioral and structural model in verilog is that behavioral model describes the system in an algorithmic manner, while structural model describes the system using basic components such as logic gates generally, a computer program is a set of instructions that allows the cpu to perform a task. Verilog is based on c, while vhdl is based on pascal and ada. Verilog and vhdl share common characteristics clear separation between concurrent and sequential domain, concurrent semantic delta time, and software constructs subprograms. The difference in case of asic is that the resultant circuit is permanently drawn into silicon whereas in fpgas the circuit is made by connecting a number of configurable blocks. In contrast, both verilog and vhdl make a difference between an unsigned and a signed representation. Actually, that mapping had to be mediated by our circuit knowledge, as no code backreference7 was available. What is the difference between verilog and vhdl answers.
Comparison of vhdl and verilog there are now two industry standard hardware description languages, vhdl and verilog. I want to know whats the difference between the case, casex, casez and its counterpart if conditional statement, in their execution. Unlike vhdl, all data types used in a verilog model are defined by the verilog language and not by the user. You can provide multple verilog files even with wildcard like. Verilog macros are simple text substitutions and do not permit arguments.
Whats the difference between vhdl, verilog, and systemverilog. Vhdl libraries contain compiled architectures, entities, packages, and configurations. Systemverilog has all the dynamic software programming features that you need to create a testbench, and the objectoriented programming features to make that testbench reusable. These errors do not occur for the verilog code in the mixed simulation, so icarus is indeed performing as it should with respect to the verilog code. Difference between vhdl, verilog and system verilog.
If you are only talking about the verification domain, then the comparison needs to be between vhdl and systemverilog, not verilog. Jun 24, 2015 majority of the operators are same between the two languages. The vhpi allows tools programmable access to a vhdl model before and during simulation. The next revision of vhdl was released in january 2009, and is referred to as vhdl 2008. On the contrary, vhdl has the mod operator that is not found in verilog. Explain difference between signal and variable in vhdl. Vhdl is very deterministic, where as verilog is nondeterministic under certain circumstances. The 1st case is logical equality and will only evaluate to a 1 if both a and b are equal to logic values of 0 or 1. Verilog looks closer to a software language like c. When youre coding a program with vhdl, it can seem to flow better.
You may find there are no inputoutput ports defined in top level behavioural modules, since the output may be to. What interview questions are asked on vhdl and verilog. The boundary between vhdl and verilog is enforced at design unit level. In other words, you can write programs in a language such as c that interact with a vhdl simulator.
Understanding verilog blocking and nonblocking assignments. Signals are used as interconnects between components and also to store temporary values. For high level behavioral modeling, vhdl is better verilog does not have ability to define new data types other missing features for high level modeling verilog has builtin gate level and transistor level primitives. This makes it easier for someone who knows c well to read and understand what verilog is doing. Verilog has very simple data types, while vhdl allows users to create more complex data types.
Here we provide some useful background information and a tutorial, which explains the basics of verilog from a hardware designers perspective. The highlighted differences allowed us to focus our attention on a restricted section of code where the difference happened. Icarus verilog has a vhdl target code generator that is being actively maintained. There are some similarities, but they are overshadowed by their differences. A loop statement can be used in vhdl to perform the same operation as a verilog unary reduction operator. Digital logic design at the time was mostly hand designed, gates, and flops and connect them all. This feature is very useful when managing large design structures. What is the difference between behavioral and structural. The verilog hdl is an ieee standard hardware description language. Vhdl and verilog by comparing their similarities and contrasting their diffrences. These languages are used in electronic devices that do not share a computers basic architecture.
The difference between integer operations and fractional operations is in the overflow. Both languages are a layer on top of gates and flops. Franzon, verilog styles of digital systems, prentice hall, inc. With vhdl, you have a higher chance of writing more lines of code. It is not currently and may never be a general purpose verilog to vhdl converter. Vhdl to verilog i dont often convert vhdl to verilog but when i do it is not the most exciting task in the world that is an understatement. Verilog assumes that whatever you wrote was exactly what you intended to write. Appendix b is a good cross reference for the two description languages. The testbench cannot create an instance of the vhdl code due to the errors. For this reason it is a good reference for anyone knowing vhdl or verilog and wishing to quickly learn the other language for synthesis. Vhdl can be viewed as a language written in programmers point of view. I dont often convert vhdl to verilog but when i do. For verilog, successful compilation merely indicates that the syntax rules were met, nothing more.
Topdown design approach definition of module some points to remember description of module the module interface one language, many coding style one language, many coding style contd. With experience you can tell them apart quickly, heres a few traits of each. Later, vhdl was developed under contract from darpa. For this reason an existing c programmer may prefer verilog over vhdl. Generally i use it when i design some program logic along with the. Full adder in verilog this tutorial is intended to familiarize you with the altera environment and introduce the hardware description languages vhdl and verilog. Vhdl is case insensitive, vhd2vl is case retentive, and verilog is case sensitive. Verilog lacks the library management, like that of vhdl.
If you need a refresher, try this page about vhdl variables. Fpgas have actually make hardware based data path and alu design on hardware. As a result, designs written in vhdl are considered selfdocumenting. Verilog and vhdl are hardware description languages that are used to write programs for electronic chips. As a result, vhdl is a strongly typed, verbose, deterministic language. Vhdl is a system level programming language and verilog is a circuit level programming language. We will, however, allow the use of behavioral constructs when writing the test procedures, called test benches. Vhdl is more verbose than verilog and it is also has a nonc like syntax. Prentice hall, 2003 vhdl tutorial, jan van derspiegel, university of pennsylvania, department of electrical and systems engineering wikipeidia. Functional simulation can be performed at that level, providing orders of magnitude acceleration over vhdl or verilog simulation. Compared to vhdl, verilog data types a very simple, easy to use and very much geared towards modeling hardware structure as opposed to abstract hardware modeling. It is widely used in the design of digital integrated circuits. Tell us what confuses you, what you have tried, and fix the tags.
441 590 1168 527 754 955 968 139 1445 137 415 333 288 476 322 1277 967 88 345 1517 106 126 54 1148 1186 901 719 1358 574 203 336 413