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

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

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

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

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

RLC : Rotate Left with carry RRC : Rotate Right with carry Carry : 1 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 9/23/2006 DSD,USIT,GGSIPU

Adding Operators + addition - subtraction & Concatenation Example: C <= a & b; c = 10101000 C <= b & a; c := 10001010 9/23/2006 DSD,USIT,GGSIPU

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

Miscellaneous Operators Abs Absolute ** Exponentiation Not negation 9/23/2006 DSD,USIT,GGSIPU

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

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

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’ 9/23/2006 DSD,USIT,GGSIPU

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 Type bit8 is 255 downto 0 bit8’high is 255 9/23/2006 DSD,USIT,GGSIPU

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 9/23/2006 DSD,USIT,GGSIPU

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