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Operators

Operators. Assignment Operators Logical Operators Relational Operators Shift Operators Adding Operators Multiplying Operators Miscellaneous Operators. Assignment Operators. Used to assign values to signals, variables and constants. <= Used to assign a value to a Signal

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Operators

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  1. Operators • Assignment Operators • Logical Operators • Relational Operators • Shift Operators • Adding Operators • Multiplying Operators • Miscellaneous Operators DSD,USIT,GGSIPU

  2. Assignment Operators • Used to assign values to signals, variables and constants. <= Used to assign a value to a Signal := Used to assign a value to a variable, constant, or Generic Must be the same size and type => Used to assign values to individual vector elements or with OTHERS. DSD,USIT,GGSIPU

  3. Logical Operators • The seven Logical Operators • AND • OR • NAND are not associative • NOR are not associative • XOR • XNOR • NOT ; highest precedence over the others DSD,USIT,GGSIPU

  4. Relational Operator • = Equality • /= inequality • < • <= • > • >= • Must be one-dimensional discrete array of the same type. DSD,USIT,GGSIPU

  5. Shift Operators • Sll Shift left logical • Srl Shift right logical • Sla Shift left arithmetic • Sra Shift right arithmetic • Rol Rotate left • Ror Rotate Right DSD,USIT,GGSIPU

  6. A = 10101100 • B <= rol a, -2; • B = 10110011 • B <= 00111011 • B <= sla a, 3 b <= 01100000 • B<= sra a, 2 b <= 11101011 • RLC : Rotate Left with carry • RRC : Rotate Right with carry • Carry : 1 B <= Rlc a, 2 B <= 10110011 carry : 0 DSD,USIT,GGSIPU

  7. Adding Operators • + addition • - subtraction • & Concatenation • Example: • A = 1010 • B = 1000 • C <= a & b; c = 10101000 • C <= b & a; c := 10001010 DSD,USIT,GGSIPU

  8. Multiplying Operators • * Multiplication • / Division • Mod modulus • Rem Remainder DSD,USIT,GGSIPU

  9. Miscellaneous Operators • Abs Absolute • ** Exponentiation • Not negation DSD,USIT,GGSIPU

  10. Attributes • An attributes is a value, function, type, range, signal or a constant that may be associated with one or more names within a VHDL description. • Two types of attributes • User defined attributes • Predefined attributes DSD,USIT,GGSIPU

  11. Classes of attributes • Value attributes : Return a constant value • Function attributes : Call a function that return a value • Signal Attributes : Creates a new implicit signal • Type Attributes : Return a type • Range attributes : Returns a range To use a attribute the “’” (apostrophe) construct must be employed DSD,USIT,GGSIPU

  12. Type Attributes • T’Base Returns the base type of datatype it is attached to example: Natural’base returns integer • T’Left Returns left value specified in type declaration Example: Integer’Left is –2147483647 Bit’left is ‘0’ DSD,USIT,GGSIPU

  13. T’right Returns right value specified in type declaration Example: Integer’right is 2147483647 bit’right is ‘1’ • T’high Returns largest value specified in declaration Example: Type bit8 is 255 downto 0 bit8’high is 255 DSD,USIT,GGSIPU

  14. T’low Returns smallest value specified in declaration Example: Type bit8 is 255 downto 0; bit8’low is 0; • T’pos(x) Returns position number of argument in type (first position is 0) Example: Type color is (red,green, blue, orange); color’pos(green) is 1; DSD,USIT,GGSIPU

  15. T’val(x) Returns value in type at specified position number Example: Type color is (red,green, blue, orange); color’val(3) is orange; • T’succ(x) Returns the successor to the value passed in Example: Type color is (red,green, blue, orange); color’succ(green) is blue; DSD,USIT,GGSIPU

  16. T’pred(x) Returns the predecessor to the value passed in Example: Type color is (red,green, blue, orange); color’pred(blue) is green; • T’leftof(x) Returns the value to the left of the value passed in Example: Type color is (red,green, blue, orange); color’leftof(blue) is green DSD,USIT,GGSIPU

  17. T’rightof(x) Returns the value to the right of the value passed in Example: Type color is (red,green,blue,orange); color’rightof(blue) is orange; Type s is (1,0,0,1,0,1) S’rightof(1) DSD,USIT,GGSIPU

  18. Signal attributes • S’event • Function returning a boolean that identifies if signal S has a new value assigned onto this signal (I.e. value is different that last value) • Returns TRUE when an event occurs on s. • If clk’event then …….– if clk just changed in value than… • Wait until clk’event and clk=‘1’ ;-- rising edge of clock DSD,USIT,GGSIPU

  19. Signal attribute (cont..) • S’stable • Implicit signal of Boolean type. This implicit signal has the value TRUE when an event (change in value) has not occurred on signal S for T time units and the value FALSE otherwise. If time is omitted, it defaults to 0ns. • Returns TRUE if no event has occurred on s • If s’stable(40ns) then – met set up time DSD,USIT,GGSIPU

  20. S’active • S’active • Function returning a boolean that identifies if signal S had a new assignment made onto it (whether the value of the assignment is the SAME or DIFFERENT). • Returns TRUE if s = ‘1’ • If s’active then…….– New assignment of S • Wait on s’active; • Wait until s’active; DSD,USIT,GGSIPU

  21. Signal attribute (cont..) • S’quiet <time> • This implicit signal has the value TRUE when the signal has been quiet (I.e. no activity or signal assignment) for T time units, and the value FALSE otherwise. If time is omitted, it defaults to 0ns. • Returns TRUE if no event has occurred during the time specified • If s’quiet(40ns) then – Really quiet, not even an assignment of the same value during the last T time units. DSD,USIT,GGSIPU

  22. Signal attributes (cont..) • S’Last_event • Function returning the amount of time that has elapsed since the last event (change in value) occurred on signal S. If there was no previous event, it returns Time’high (The maximum value for time) • Returns the time elapsed since last event • Variable : TsinceLastEvent:time; • …. • TsinceLastEvent :s’last_event; DSD,USIT,GGSIPU

  23. S’Last_active • Returns the time elapsed since last s=‘1’ DSD,USIT,GGSIPU

  24. Signal attribute (cont.) • S’last_value • Returns the value of s before the last event • S’transaction • Signal of type bit that changes for every transaction on s • S’delayed<time> • Signal same as s delayed by specified time DSD,USIT,GGSIPU

  25. User-defined Attributes • Syntax • Attribute Declaration: • ATTRIBUTE attribute_name: attribute_type; • Attribute specification: • ATTRIBUTE attribute_name of target_name : class is value; Where: Attribute_type : any data type (bit,std_logic etc) Class : type, signal,function etc. Value : ‘0’, 27, “000101110” , etc DSD,USIT,GGSIPU

  26. Generic • Generic is a way of specifying a generic parameter • A static parameter that can be easily modified and adapted to different applications. • A generic statement, when employed must be declared in the entity. Syntax: Generic (parameter_name : parameter_type:= parameter_value); DSD,USIT,GGSIPU

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