Verilog Hex to Seven Segment Display |
We will be moving on to write slightly more complex example, this time a hex to seven segment encoder. Basically LED number is displayed with 7 segments.
The hexadecimal to 7 segment encoder has 4 bit input and 7 output. Depending upon the input number, some of the 7 segments are displayed. The seven segments are represented as a,b,c,d,e,f,g. A high on one of these segements make it display. For example to write 1 we need to display segments b and C.
The 7 segment display also has a decimal point dp.
The figure below explains this Let write this example making use of the verilog case statement
Note that we had to assign out as a register in
reg out;
In our case, it was not required because we had only one statement. We now suggest that you write a test bench for this code and verify that it works. If you have sifficulty, you can check it with following test bench
Exercise |
1. Change the above hex to BCD verilog code so that it take negative logic. A segment is on when it gets 0. A segment is off when it gets logic 1.
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There are so many resources online talking about how to represent and extend signed numbers in Verilog, but I still can not get it. Let's say I have a number 244, which is 'b1111_0100, or 'hF4. If I want to represent this number in signed decimal, should I need to declare the size with one extra bit for the sign?
Even more confusion comes with negative numbers: do I need to represent them in 2's complement format? How about the size? It would be nice if someone could give an explanation with example in the
NazarNazar<size>'<signed><format><value>
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$endgroup$3 Answers
$begingroup$To declare a negative number in 2's complement form, you place the negative sign in front of the width specifier, for example
Would be the value of -16, and would have the same bit pattern as the unsigned value
8'HF0
You do indeed need to include the sign bit in your width considerations, and it is of course essentially up to you to keep track of which vectors are to to be interpreted as signed and which as unsigned.
Chris StrattonChris Stratton24.6k22 gold badges3030 silver badges6969 bronze badges
$endgroup$$begingroup$You need to separate the bit-pattern value expressed by a numeric literal from signed or unsigned type. Signedness only comes into play when a value gets used in another expression, and it also determines the interpreted minimum/maximum values. The
<size>
, <radix>
, and <value>
parts of a literal give you an unsigned bit pattern. If you are working with an 8-bit expression, the largest signed value you can represent is 127. So if you have 8'sd244, that will be interpreted as a signed negative number(-11, I think). If you are trying to represent -244, you need at least a 9-bit wide value. Verilog has tricky rules when mixing signed and unsigned data types. But in general, the MSB of a signed expression gets sign-extended when used in a larger width signed expression.
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$endgroup$$begingroup$For representing signed numbers, you definitely need 1 extra bit, like if +250 in unsigned could be represented in 8 bits but both +250 and -250 when declared unsigned would need 9 bits.
You can try out this small program and see yourself
So, +250 when represented in 8 bits (unsigned), if done 2's complement does not produce -250. To get -250, you need 9 bits and that when 2's complemented produces -250 correctly.
Shankhadeep MukerjiShankhadeep Mukerji
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To use this hex to binary converter tool, just type a hex value like 1E into the left field below, and then hit the Convert button. Therefore, you can convert up to 16 hex characters (max. value of 7fffffffffffffff).
Hex to binary conversion result in base numbers
Hex System
Hex, or hexadecimal, is a number system of base 16. This number system is especially interesting because in our casually used decimal system we have only 10 digits to represent numbers. As hex system has 16 digits, the extra needed 6 digits are represented by the first 6 letters of English alphabet. Hence, hex digits are 0,1,2,3,4,5,6,7,8 and 9 A, B, C, D, E, F. This number system is the most commonly used in mathematics and information technologies. I.e. in html programming colors can be represented by a 6-digit hexadecimal number: FFFFFF represents white, 000000 represents black, and so on.
Binary System
The binary numeral system uses the number 2 as its base (radix). As a base-2 numeral system, it consists of only two numbers: 0 and 1.
While it has been applied in ancient Egypt, China and India for different purposes, the binary system has become the language of electronics and computers in the modern world. This is the most efficient system to detect an electric signal’s off (0) and on (1) state. It is also the basis for binary code that is used to compose data in computer-based machines. Even the digital text that you are reading right now consists of binary numbers.
Reading a binary number is easier than it looks: This is a positional system; therefore, every digit in a binary number is raised to the powers of 2, starting from the rightmost with 20. In the binary system, each binary digit refers to 1 bit.
Verilog Decimal To Binary Converter
How to Read a Binary Number
In order to convert binary to decimal, basic knowledge on how to read a binary number might help. As mentioned above, in the positional system of binary, each bit (binary digit) is a power of 2. This means that every binary number could be represented as powers of 2, with the rightmost one being in the position of 20
Example: The binary number (1010)2 can also be written as follows:
(1 * 23) + (0 * 22) + (1 * 21) + (0 * 20)
Hex to binary conversion examples
- (1E3)16 = (0001 1110 0011)2
- (0A2B)16 = (0000 1010 0010 1011)2
- (7E0C)16 = (0111 1110 0000 1100)2
Related converters: Binary To Hex Converter
Hexadecimal to Binary Conversion Chart
Hexadecimal | Binary |
---|---|
0 | 0000 |
1 | 0001 |
2 | 0010 |
3 | 0011 |
4 | 0100 |
5 | 0101 |
6 | 0110 |
7 | 0111 |
8 | 1000 |
9 | 1001 |
A | 1010 |
B | 1011 |
C | 1100 |
D | 1101 |
E | 1110 |
F | 1111 |
Binary to BCD Converter
Some times we need to display the output in a seven-segment display. For that purpose we will convert binary to BCD.
To translate from binary to BCD, we can employ the shift-and-add-3 algorithm:
Left-shift the (n-bit) binary number one bit.
If n shifts have taken place, the number has been fully expanded, so exit the algorithm.
If the binary value of any of the BCD columns is greater than or equal to 5, add 3.
Return to (1).
If n shifts have taken place, the number has been fully expanded, so exit the algorithm.
If the binary value of any of the BCD columns is greater than or equal to 5, add 3.
Return to (1).
VHDL Code for Binary to BCD Converter
VHDL Teshbench Code for Binary to BCD Converter
Simulation Waveform Result for Binary to BCD Converter
Lexical conventions in Verilog are similar to C in the sense that it contains a stream of tokens. A lexical token may consist of one or more characters and tokens can be comments, keywords, numbers, strings or white space. All lines should be terminated by a semi-colon
;
.Verilog is case-sensitive, so var_a and var_A are different.
Comments
There are two ways to write comments in Verilog.
Click Service Select Hide All Microsoft Services check box and then click Disable All OK. Sfc scannow error windows resource protection could not perform the requested operation.
- A single line comment starts with
//
and tells Verilog compiler to treat everything after this point to the end of the line as a comment. - A multiple-line comment starts with
/*
and ends with*/
and cannot be nested.
However, single line comments can be nested in a multiple line comment.
Whitespace
White space is a term used to represent the characters for spaces, tabs, newlines and formfeeds, and is usually ignored by Verilog except when it separates tokens. In fact, this helps in the indentation of code to make it easier to read.
However blanks(spaces) and tabs (from TAB key) are not ignored in strings. In the example below, the
string
variable called addr gets the value 'Earth ' because of preservation of spaces in strings.Operators
There are three types of operators: unary, binary, and ternary or conditional.
- Unary operators shall appear to the left of their operand
- Binary operators shall appear between their operands
- Conditional operators have two separate operators that separate three operands
If the expression (y > 5) is true, then variable x will get the value in w, else the value in z.
Number Format
We are most familiar with numbers being represented as decimals. However, numbers can also be represented in binary, octal and hexadecimal. By default, Verilog simulators treat numbers as decimals. In order to represent them in a different radix, certain rules have to be followed.
Sized
Sized numbers are represented as shown below, where size is written only in decimal to specify the number of bits in the number.
- base_format can be either decimal ('d or 'D), hexadecimal ('h or 'H) and octal ('o or 'O) and specifies what base the number part represents.
- number is specified as consecutive digits from 0, 1, 2 .. 9 for decimal base format and 0, 1, 2 . 9, A, B, C, D, E, F for hexadecimal.
Uppercase letters are legal for number specification when the base format is hexadecimal.
Unsized
Numbers without a base_format specification are decimal numbers by default. Numbers without a size specification have a default number of bits depending on the type of simulator and machine.
Negative
Negative numbers are specified by placing a minus
-
sign before the size of a number. It is illegal to have a minus sign between base_format and number.Strings
Decimal To Octal
A sequence of characters enclosed in a double quote
' '
Samsung usb driver for windows 10. is called a string. It cannot be split into multiple lines and every character in the string take 1-byte to be stored.Identifiers
Identifiers are names of variables so that they can be referenced later on. They are made up of alphanumeric characters
[a-z][A-Z][0-9]
, underscores _
or dollar sign $
and are case sensitive. They cannot start with a digit or a dollar sign.Keywords
Keywords are special identifiers reserved to define the language constructs and are in lower case. A list of important keywords is given below.
Verilog Revisions
Verilog has undergone a few revisions over the years and more additions have been made from 1995 to 2001 which is shown below.