![]() In this chain of assignments, when a= 101, it is sign-extended so that b= 1101, but since b is unsigned it is zero extended to 01101, resulting in c= 01101 (+13). Reg signed a reg b reg c always begin b = a c = b end Sometimes we need to do operations on vectors of different bit width. Is there an efficient way to detect overflow cases? Give a precise logic solution that detects all overflow events. Study the results from the 3-bit addition table. Do the addition using binary arithmetic, and indicate overflow cases with an exclamation point (!). For each entry, write the binary result and, in parentheses, the decimal interpretation. Pos DecĬomplete the binary addition table below. ![]() Exercise: 4-bit 2’s Comp Negation TableĬomplete the negative values in the table below. In Verilog syntax, these steps are expressed as ~N+ 1 or just -N. Add 1 to ~N using normal addition, discarding the final carry.2E12 (the exponent symbol can be e or E )Ģ36.In 2’s Complement, a negative number -N is obtained from a positive number N by two steps: ![]() 4'sd15 // this is equivalent to -(-4~Rd 1), or ~Q0001~R.ĮXAMPLE: Using underscore character in numbersġ. be interpreted as a 2~Rs complement number, held in 8 bits~Wequivalent to -(8~Rd 6)Ĥ'hf // this denotes the 4-bit number ~Q1111~R, to 8'd 6 // this defines the two~Rs complement of 6, Some examples of valid numbers are:Ĥaf // is illegal (hexadecimal format requires ~Rh)ģ'b01x // is a 3-bit number with the leastġ6'hz // is a 16-bit high-impedance numberĮXAMPLE: Using sign with constant numbers The X's mean unknown, and the Z's mean high impedance If no base format is specified the number is assumed to be a decimal number. Numbers consist of strings of digits (0-9, A-F, a-f, x, X, z, Z). Valid base formats are 'b, 'B, 'h, 'H 'd, 'D, 'o, 'O for binary, hexadecimal, decimal, and octal. If no is specified then the default size is at least 32bits and may be larger depending on the machine. ![]() The size is always specified as a decimal number. Number : Numbers in verilog are in the following format. You can access any word as m for example but you do not get access to the bits in the word unless you copy the word to another 8-bit reg variable. For example reg m declares m to be a two-dimensional array consisting of 64 eight-bit words. Memory : Verilog allows for two dimensional arrays which typically get used for memory spaces. Here are some typical parameter examples: Parameter declarations are done immediately after the module declaration. For example a 4-bit adder becomes more useful as a design if it is put together as an n-bit adder where n is a parameter specified by the user before compilation. Parameters are used to generalize a design. Parameters : a parameter in Verilog can be any Verilog constant. These are 0 (logic 0), 1 (logic 1), ?, X, or x ( don~Rt care or unknown), and Z or z for high impedance tri-state. Signal values : signals in Verilog have one of four values. As in C++ variable names should be chosen to assist in documentation. Identifiers may not begin with a digit and may not be the same as a Verilog key word. You can use any letter, digit, the underscore, or $. Identifiers : An identifier is usually a variable. A semicolon is used to indicate the end of a command line and commas are typically used to separate elements in a list. Punctuation : white spaces are ignored in Verilog. Use // for a single line comment or /* */ for a multiline comment. Comments : Verilog comments are the same as in C++.
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