Data Types

1
Data Types
2
Composite Date Types

• Arrays
• Single and multi-dimensional
• Arrays are single Type
• Records
• Records are mixed types

3
Array

• Array is an Indexed Collection of Elements All of
  the Same Type
• One-dimensional with one index
• Multi-dimensional with several indices

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Constrained versus unconstrained Arrays

• Constrained
• the bounds for an index are established when the
  type is defined
• Unconstrained
• the bounds are established after the type is
  defined
• Each position in the array has a scalar index
  value associated with it

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Array Definition Syntax and Example

• array ( discrete_range , ... )
• of element_subtype_indication
• discrete_range is an index
• name of previously declared type with optional
  range constraint

type Large_Word is array ( 63 downto 0 ) of bit
type Address_List is array ( 0 to 7 ) of
Large_Word
Example 1
Example 2
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More examples of Array Declaration
array ( discrete_range , ... ) of
element_subtype_indication

• type 2D_FFT is array
• ( 1 to 128, 1 to 128 ) of real
• type Scanner is array
• ( byte range 0 to 63 ) of integer
• type Sensor_Status is array
• ( Stdby, On, Off ) of time

7
Unconstrained Declaration of array

• type Detector_Array is array
• ( natural range ltgt ) of natural
• The symbol ltgt is called a box and can be
  thought of as a place-holder for the index range.
• Box is filled in later when the type is used.
• variable X_Ray_Detector Detector_Array
• ( 1 to 64 )

8
Two Examples of Predefined Unconstrained Types

• type string is array
• ( positive range ltgt ) of character
• type bit_vector is array
• ( natural range ltgt ) of bit

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Two more Examples of Predefined Unconstrained
Types

• type std_ulogic_vector is array
• ( natural range ltgt ) of std_ulogic
• type bit_vector is array
• ( natural range ltgt ) of bit

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Unconstrained Array Ports
You do the following

• 1. Specify Port as unconstrained
• 2. Determine size of port by Index Bounds of
  Signal
• e.g., AND Gates With Different Number of Inputs

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1. Example of entity of Unconstrained Array Port
You specify vector of bits with no number here

• entity And_Multiple is
• port ( i in bit_vector
• y out bit )
• end entity And_Multiple

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2. AND, example continued

• architecture And_Multiple_B of
• And_Multiple is
• begin
• And_Reducer process ( i ) is
• variable Result bit
• begin
• Result 1
• for Index in iRange loop
• Result Result and i ( Index )
• end loop

You use Range so you still do not tell how many
bits
variable
Signal created outside the loop
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AND, example continued

• y lt Result
• end process And_Reducer
• end architecture And_Multiple_B

signal
Here we finished architecture And_Multiple_B
without specifying number of bits
In the next slide we will call this architecture
structurally and at this time the number of bits
will be decided
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AND, e.g.,
count_value 8 bits
terminal_count

• signal count_value
• bit_vector ( 7 downto 0 )
• signal terminal_count bit
• tc_gate entity work.And_Multiple
• ( And_Multiple_B )
• port map ( i gt count_value ,
• y gt terminal_count )

architecture And_Multiple_B

• The Input Port Is Constrained by the Index Range
  of the Input Signal, i.e., An 8-Input AND Gate.

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Array References

• Arrays Can Be Equated, Rather Than Having to
  Transfer Element by Element
• Refer to Individual Elements By
• 1. Single Index Value, e.g., A ( 5 )
• 2. Range a contiguous sequence of a
  one-dimensional array can be referred to by using
  it as an index. e.g., A( 5 to 15 )
• 3. Previously defined subtype
• 4. Index types do not have to be the same

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Examples of Array Aggregate
Sensor_Status
Stdby
On
Off

• type Sensor_Status is
• array ( Stdby , On , Off ) of time
• variable FLIR_Status
• Sensor_Status ( 0 sec , 0 sec , 0 sec )
• variable FLIR_Status
• Sensor_Status ( On gt 5 sec )

Changes only one field
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Array Aggregate Syntax

• A List of Element Values Enclosed in Parentheses
• This list is used to initialize Elements of an
  Array to Literal Values
• aggregate lt ( choices gt
• expression ... )

type Sensor_Status is array ( Stdby , On , Off
) of time
syntax
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There are two ways to refer to elements in Array
Aggregate

• Two Ways of Referring to Elements
• Positional explicitly list values in order
• Named Association Explicitly list values by
  their index using choices
• Order NOT important
• Positional and Named Association Cannot Be Mixed
  Within an Aggregate.

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Example of Named Association in Array Aggregate

• others Can Be Used in Place of an Index in a
  Named Association,
• Indicating a Value to Be Used for All Elements
  Not Explicitly Mentioned
• variable FLIR_Status Sensor_Status
• ( Off gt 10 min, others gt 0 sec )

Named Association Explicitly list values by
their index using choices Order NOT important
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Example of setting many elements to one value in
Array Aggregate
Here I set 4 elements of array to 1 all other to 0

• A Set of Values Can Be Set to a Single Value by
  Forming a List of Elements Separated by Vertical
  Bars, .
• type 2D_FFT is array
• ( 1 to 128, 1 to 128 ) of real
• variable X_Ray_FFT 2D_FFT
• ( ( 60, 68 ) ( 62, 67 ) ( 67, 73 ) ( 60,
  60 ) gt 1.0 , others 0.0 )

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Array Operations element by element logic
operations

• One-Dimensional Arrays of Bit or Boolean
• Element by element AND, OR, NAND, NOR, XOR, XNOR
  can be done on array
• type Large_Word is array
• ( 63 downto 0 ) of bit
• variable Samp_1 , Samp_2 Large_Word
• ( 0 to 63 gt 0 )

Here we declare variables Samp_1 and Samp_2 that
we will use next
0
Large_Word
0
63
0
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Array Operations element by element logic
operations

• constant Bit_Mask Large_Word
• ( 8 to 15 gt 1 )
• Samp_2 Samp_1 and Bit_Mask

Bits from 8 to 15 are AND-ed with Bit_Mask
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NOT Operations
Array Operations element by element logic
operations

• Complement of elements of a single array, NOT
• Samp_2 not Samp_1

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1D Shift and Rotate Array Operations

• One-Dimensional Arrays Can Be Shifted and Rotated
• Shift
• Logical Shifts and fills with zeros
• Arithmetic Shifts and fills with copies from
  the end being vacated
• Rotate
• Shifts bits out and back in at other end

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Shift and rotate operations
Shift left logic

• B 1010_1100 sll 4 B 1100_0000
• B 1010_1100 sla 4 B 1100_0000
• B 1010_1100 sra 4 B 1111_1010
• B 1010_1100 rol 4 B 1100_1010

Rotate left
Shift right arithmetic
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Relational Array Operations

• One-Dimensional Arrays Can Be Operated on by
  Relational Operators,
• , / , lt , lt , gt ,
  gt
• Arrays need not be of the same length
• Arrays must be of same type

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Array Operations Concatenation

• Concatenation Operator,
• Can combine array and scalar
• B 1010_1100 B 1100_0000
• B 1010_1100_1100_0000
• B 1010_1100 1 B 1010_1100_1

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Conversion from one Array Type to another

• One Array Type Can Be Converted to Another If
• Same element type
• Same number of dimensions
• Same index types

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Example of Array Type Conversions

• Example
• subtype name is string ( 1 to 20 )
• type display_string is array ( integer range 0 to
  19 ) of character
• variable item_name name
• variable display display_string
• display display_string ( item_name )

1 to 20
0 to 19
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Example of Array Aggregate

• Assignments Can Be Made From a Vector to an
  Aggregate of Scalars or Vice-Versa.
• type Sensor_Status is array
• ( Stdby, On, Off ) of time
• variable Stdby_Time, On_Time, Off_Time time

Variable FLIR_Status Sensor_Status ( 0
sec , 0 sec ,
0 sec ) ( Stdby_Time, On_Time,
Off_Time ) Flir_Status
Aggregate of scalars
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Predefined Attributes

• Predefined Attributes deal with data obtained
  from Blocks, Signals, Types and Subtypes
• Return values such as
• length of an array type
• time since last signal change
• range of values in a type
• Predefined attributes are useful for performing
  certain type of functions such as
• timing checks
• bounds
• clock edge detection
• type conversion

We showed earlier attributes for signals. Now we
show for types
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Array Type Bound Example use of predefined
attributes
attribute
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Another Example of array bound
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Multi-range array attributes
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Array length attributes
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Range attributes
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Type attributes position function
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Homework Attributes Exercise
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Example of using Attributes
We calculate resistance dividing voltage by
current
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User Defined Attributes

• These attributes attach data to objects
• They are defined by the user of Data types
• Data is constant
• They are accessed with the same syntax as
  predefined attributes

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User Defined Attributes
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Records

• Records in VHDL are collections of Named Elements
  of Possibly Different Types.
• To refer to a Field of a Record Object, you
  should use a Selected Name.

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Example of a Record

• type instruction is
• record
• op_code processor_op
• address_mode mode
• operand1, operand2
• integer range 0 to 15
• end record

Ashenden, VHDL cookbook
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Records

• Aggregates Can Be Used to Write Literal Values
  for Records.
• Positional and Named Association Can Be Used
• Record field names being used in place of array
  index names.

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End of Lecture
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Sources

• Prof. K. J. Hintz
• Department of Electrical
• and
• Computer Engineering
• George Mason University