Find the most up-to-date version of IEEE at Engineering DRAFT. Summary of Key Verilog Features (IEEE ) ∗. Module. Encapsulates functionality; may be nested to any depth module module name (list of ports);. What this means, however, is that two different Verilog standardization efforts will be ongoing. One is IEEE , an upcoming revision of the IEEE.
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The advent of hardware verification languages such as OpenVeraand Verisity’s e language encouraged the development of Superlog by Co-Design Automation Inc vrrilog by Synopsys.
A Verilog design consists of a hierarchy of modules. Hardware iCE Stratix Virtex. The initial keyword indicates a process executes exactly once. This condition may or may not be correct depending on the actual flip flop.
Verilog requires that variables be given a definite size. The most common of these is an always keyword without the Synthesis software algorithmically transforms the abstract Verilog source into a netlista logically equivalent description consisting only of elementary logic primitives AND, OR, NOT, flip-flops, etc. The PLI now VPI enables Verilog to cooperate with other programs written in the C language such as test harnessesinstruction set simulators of a microcontrollerdebuggersand so on.
Signals that are driven from outside a process must be of type wire. Verilog is a portmanteau of the words “verification” verrilog “logic”. What will be printed out for the values of a and b? Depending on 13664 order of execution of the initial blocks, it could be zero and zero, or alternately zero and some other arbitrary uninitialized value. Views Read Edit View history. This section presents a short list of the most frequently used tasks.
The always block then executes when set goes high which because reset is high forces q to remain at 0. Su, for his PhD work.
It is also used in the verification of analog circuits and mixed-signal circuitsas well as in the design of genetic circuits. At the time of Verilog’s introductionVerilog represented a tremendous productivity ieed for circuit designers who were already using graphical schematic capture software and specially written software programs to document and simulate electronic circuits.
Signals that are driven from within a process an initial or always block must be of type reg.
Extensions to Verilog were submitted back to IEEE to cover the deficiencies that users had found in the original Verilog standard. A simple example of two flip-flops follows:. And finally, a few syntax additions were introduced to improve code readability e.
A subset of statements in the Verilog language are synthesizable. A variant of the D-flop is one with an asynchronous reset; there is a convention that the reset state vsrilog be the first if clause within the statement. In this example the always statement would first execute when the rising edge of reset occurs which would place q to a value of 0.
Michael; Thornton, Mitchell A.
Verilog – Wikipedia
The mux has a d-input and feedback from the flop itself. The IEEE standard defines a four-valued logic with four states: It is by no means a comprehensive list. Verilog’s concept of ‘wire’ consists of both signal values 4-state: Verilog was one of the first popular [ clarification needed ] hardware description languages to be invented. In fact, it is better to think of the initial -block as a special-case of the always -block, one which terminates after it completes for the first time.
This system allows abstract modeling of shared signal lines, where multiple sources drive a common net. It is ieee common misconception to believe that an initial block ieef execute before an always block. The examples presented here are the classic subset of the language that has a direct mapping to real gates.
This page was last edited on 1 Decemberat Verilog modules that conform to a synthesizable coding style, known as RTL register-transfer levelcan be physically realized by synthesis software. The designers of Verilog wanted a language with syntax similar to the C programming languageverilgo was already widely used in engineering software development. For information on Verilog simulators, see the list of Verilog simulators.
The basic syntax is:. Its action does not register until after the always block has executed. Assume no setup and hold violations.
The flip-flop is the next significant template; in Verilog, the D-flop is the simplest, and it can be modeled as:. Internally, a module can contain any combination of the following: The next variant is including both an asynchronous reset and asynchronous set condition; again the convention comes into play, i. There are several statements in Verilog that have no analog in real hardware, e. The next interesting structure is a transparent latch ; it will pass the input to vefilog output when the gate signal is set for “pass-through”, and captures the input and stores it upon verjlog of the gate signal to “hold”.
The non-blocking assignment allows designers to describe a state-machine update without needing to declare and use temporary storage variables. Consequently, vegilog of the language can not be used to describe hardware. These are the always and the initial keywords.