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Operators Assignment Operators Logical Operators Relational Operators

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Presentation on theme: "Operators Assignment Operators Logical Operators Relational Operators"— Presentation transcript:

1 Operators Assignment Operators Logical Operators Relational Operators
Shift Operators Adding Operators Multiplying Operators Miscellaneous Operators 9/23/2006 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. 9/23/2006 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 9/23/2006 DSD,USIT,GGSIPU

4 Relational Operator = Equality /= inequality < <= > >=
Must be one-dimensional discrete array of the same type. 9/23/2006 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 9/23/2006 DSD,USIT,GGSIPU

6 RLC : Rotate Left with carry RRC : Rotate Right with carry Carry : 1
B <= rol a, -2; B = B <= B <= sla a, b <= B<= sra a, b <= RLC : Rotate Left with carry RRC : Rotate Right with carry Carry : 1 B <= Rlc a, 2 B <= carry : 0 9/23/2006 DSD,USIT,GGSIPU

7 Adding Operators + addition - subtraction & Concatenation Example:
C <= a & b; c = C <= b & a; c := 9/23/2006 DSD,USIT,GGSIPU

8 Multiplying Operators
* Multiplication / Division Mod modulus Rem Remainder 9/23/2006 DSD,USIT,GGSIPU

9 Miscellaneous Operators
Abs Absolute ** Exponentiation Not negation 9/23/2006 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 9/23/2006 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 9/23/2006 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 – Bit’left is ‘0’ 9/23/2006 DSD,USIT,GGSIPU

13 T’right Returns right value specified in type declaration
Example: Integer’right is bit’right is ‘1’ T’high Returns largest value specified in declaration Type bit8 is 255 downto 0 bit8’high is 255 9/23/2006 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) Type color is (red,green, blue, orange); color’pos(green) is 1; 9/23/2006 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 color’succ(green) is blue; 9/23/2006 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 color’leftof(blue) is green 9/23/2006 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) 9/23/2006 DSD,USIT,GGSIPU

18 Type a_type is array(0 to 3, 7 downto 0) of bit;
A’left(n) Returns left array bound of selected index range Example: a_type’left(1) is 0 a_type’left(2) is 7 A’right(n) Returns right array bound of selected index range a_type’right(1) is 3 a_type’right(2) is 0 9/23/2006 DSD,USIT,GGSIPU

19 Type a_type is array(0 to 3, 7 downto 0) of bit;
A’high(n) Returns largest array bound value of selected index range Example: a_type’high(1) is 3 a_type’high(2) is 7 A’low(n) Returns smallest array bound value of selected index range a_type’low(1) is 0 a_type’low(2) is 0 9/23/2006 DSD,USIT,GGSIPU

20 Type a_type is array(0 to 3, 7 downto 0) of bit;
A’range Returns selected index range Example: a_type’range(1) is 0 to 3 a_type’range(2) is 7 downto 0 A’reverse_range(n) Returns selected index range reversed a_type’reverse_range(1) 3 downto 0 a_type’reverse_range(2) 0 to 7; 9/23/2006 DSD,USIT,GGSIPU

21 Type a_type is array(0 to 3, 7 downto 0) of bit;
A’length(n) Returns size of selected index range Example: a_type’length(1) is 4 a_type’length(2) is 8. 9/23/2006 DSD,USIT,GGSIPU

22 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 9/23/2006 DSD,USIT,GGSIPU

23 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 9/23/2006 DSD,USIT,GGSIPU

24 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; 9/23/2006 DSD,USIT,GGSIPU

25 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. 9/23/2006 DSD,USIT,GGSIPU

26 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; 9/23/2006 DSD,USIT,GGSIPU

27 S’Last_active Returns the time elapsed since last s=‘1’ 9/23/2006
DSD,USIT,GGSIPU

28 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 9/23/2006 DSD,USIT,GGSIPU

29 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, “ ” , etc 9/23/2006 DSD,USIT,GGSIPU

30 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); 9/23/2006 DSD,USIT,GGSIPU

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