Verilog interview questions answers, verilog interview questions, verilog interview questions page. Verilog interview questions Page 2, verilog interview questions page 3, verilog interview questions page. Verilog interview questions, how to write fsm is verilog? There r mainly 4 ways 2 write fsm code 1) using 1 process where all input decoder, present state, and output decoder r combine in one process. 2) using 2 process where all comb ckt and sequential ckt separated in different process 3) using 2 process where input decoder and persent state r combine and output decoder seperated in other process 4) using 3 process where all three, input decoder, present state. Click to view more (Also refer to tutorial section for more).
If-else Statements -verilog Tutorial
Then statement1 will help be executed (x, z and? Are don't care report values for the casex statement). Statement3 and statement4 will never be executed. Example 5 reg a; case (1'b1) a : statement1; endcase The case expression can be a constant expression. In Example 5, statement1 will be executed only if 'a' is equal to 1'b1. Important Notes The default statement is optional and it can appear only once. The parenthesis (?) can appear in expressions and it is equal to high-impedance (z) value. If don't care values are to be ignored, then the casex or casez statements should be used. The case statement can be a group of statements in the begin - end block. Both the case expression and case item expressions should have the same length. The case statement can appear only within structured procedures.
Example 3 reg blood a; casez (a) 1'b0 : statement1; 1'b1 : statement2; 1'bx : statement3; 1'bz : statement4; endcase If value of variable 'a' is 1'b0 or 1'b1 or 1'bx then statement1, statement2 or statement3 will be executed respectively. If 'a' equals 1'bz or 1'b? Then statement1 will be executed because the casez statement treats z and? As the don't-care values. Statement4 will never be executed because only the first case item, which matches with the case expression, is executed. Example 4 reg a; casex (a) 1'b0 : statement1; 1'b1 : statement2; 1'bx : statement3; 1'bz : statement4; endcase If variable 'a' is 1'b0 or 1'b1 then statement1 and statement2 will be executed respectively. If 'a' equals 1'bx or 1'bz or 1'b?
If any of the bits in the case expression or case item expression is a don't-care value then that bit position will be ignored. The don't-care value can be also specified by the question mark? which is equal to z value. Examples, example 1 reg 1:0 address; case (address) 2'b00 : statement1; 2'b01, 2'b10 pdf : statement2; default : statement3; endcase, if the address value is 2'b00 then statement1 will be executed. Statement2 is executed when address value equals 2'b01 or 2'b10. Otherwise statement3 is executed. Example resume 2 reg a; case (a) 1'b0 : statement1; 1'b1 : statement2; 1'bx : statement3; 1'bz : statement4; endcase, in Example 2, the statements will be executed depending on the value of the 'a' variable (if a 1'b0 then statement1 will be executed, etc). If we assign a question mark (?) to the 'a' variable, then statement4 will be executed because the syntax concerning numbers defines the question mark as equal to the z value.
If all comparisons fail and the default section is given, then its statements are executed. Otherwise none of the case items will be executed. Both case expression and case item expressions should have the same bit length. None of the expressions are required to be a constant expression. The case expression comparison is effective when all compared bits are identical. Therefore, special types of case statement are provided, which can contain don't-care values in the case expression and in the case item expression. These statements can be used in the same way as the case statement, but they begin with the keywords casex and casez. The casez statement treats high-impedance (z) values as don't-care values and the casex statement treats high-impedance and unknown (x) values as don't care values.
If-else and case statements - eda playground
To observe the changes in the output waveform, we need to include this delay. If we observe the output, we can notice that input changes in the intervals of 5ns and we will get corresponding anded output in t_y. Formal Definition, the case essay statement is a decision instruction that chooses one statement for execution. The statement chosen is one with a value that matches that of the case statement. Simplified essay Syntax case (expression) expression : statement expression, expression : statement default : statement endcase casez (expression) expression : statement expression, expression : statement default : statement endcase casex (expression) expression : statement expression, expression : statement default : statement endcase, description, the case statement. It ends with the endcase keyword.
The default statement is optional and should be used only once. A case item contains a list of one or more case item expressions, separated by comma, and the case item statement. The case item expression and the case item statement should be separated by a colon. During the evaluation of the case statement, all case item expressions are evaluated and compared in the order in which they are given. If the first case item expression matches the case expression, then the statement which is associated with that expression is executed and the execution of the case statement is terminated. If comparison fails, then the next case item expression is evaluated and compared with the case expression.
'a' in the andgate will be connected to t_a in the andgate_tb and. If some of the statements in our code is to be executed only in the beginning of the execution, we can write them using initial block. Initial block executes only once and starts at time0. Your program may have any number of initial blocks. Initial block begins with begin and ends with end. Inside an initial block, statements will execute sequentially.
In next chapter, we will learn more about flow of execution of a program. Monitor is a system task used to display the values in variable whenever value of one of its arguments changes. After that we will assign different values to t_a and t_b. Here 1'b0 indicates a low signal and 1'b1 represents a high signal. Meaning of this notation is, a 1 bit variable expressed in binary. Similarly we can also indicates decimal, hex, octal numbers as follows. Integer meaning Stored as 5'b00101 5 bit binary 'b0 8 bit binary 'b101 8 bit binary 'd5 8 bit decimal 'h9f 8 bit hex 9f 'd1 3 bit decimal 1 001 4'bz 3 bit decimal z zzzz 4'bx1 binary xxx1 5'b11z binary 0011z. If value is larger than the length, left most bits will be truncated If value is smaller, 0's are filled to the left if left most bit is 0 or 1 'z' are filled if left most bit is z 'x' are filled if left.
Verilog: multiple conditions inside an if statement - altera forums
This is called instanciating by order. Here, all the ports should be in paper the order as we declared in the module definition. If we write as given in the example, we can change the order. That is, andgate my_gate(.a(t_a. Y(t_y) is equal to andgate my_gate(.b(t_b. This is called instanciation by name. Like this, we can use any number of instances of same module in a design.
testbench for and gate, file: and_tb. V module andgate_tb; wire t_y; reg t_a, t_b; andgate my_gate(.a(t_a. Y(t_y) initial begin monitor (t_a, t_b, t_y t_a 1'b0; t_b 1'b0; 5 t_a 1'b0; t_b 1'b1; 5 t_a 1'b1; t_b 1'b0; 5 t_a 1'b1; t_b 1'b1; end endmodule here we have created another module andgate_tb which will include the module andgate. We have to give values to input, so we need to store or latch the input data. So, t_a and t_b are declared as reg and t_y as wire fto get the outut value from the gate. Now, we create an instance of andgate. E., we are placing the and gate that we have created previously inside essay this module. We can use two different notations to connect the ports. We can write andgate my_gate(t_a, t_b, t_y.
and hence we did not declare any registers. By default, all the ports will be considered as wires. If we want the output to be latched, we have to declare it using the keyword 'reg'. Input a, b; output y; wire a, b, y; Next we will write a testbench to test the gate that we have created. Testbench is another verilog code that creates a circuit involving the circuit to be tested. This code will send different inputs to the code under test and get the output and displays to check the accuracy.
With this assumption, if you draw a block diagram of the circuit with a set of signals connection each other, that is called top level design. Then go on writing modules for each black box, then design that black box with in the same way. This is how we are designing a circuit. You will understand this concept after studying some examples. A module may be one gate, one flip-flop, one register, one alu one controller or one soc. Go back to the example. Here, module is keyword, andgate is the name given to the module in this examples and a, b and y are the ports or connections to the module. Every modules and with the keyword endmodule. In the beginning of a module, we have to declare all ports as input output or inout.
Ternary operator vs if else verification Academy
If you can express working of a digital circuit and visualize the flow of data inside a ic, then learning any hdl or Hardware description Language is very easy. This chapter is a overview of how Verilog code looks like. This article will always be under construction. Let us start with an and gate. Here is the truth table: a, b y a simple and gate file: and. V module andgate (a, b, y input a, b; output y; assign y a b; endmodule, now let us try to understand the code. this is multi line comment and / this is single line comment, comments are same as in C language. In verilog, one circuit is represented by set of "modules". We can consider a module as a black box.