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Data Type Conversion - Convert input signal to specified data type

Library

Signal Attributes

Description

The Data Type Conversion block converts an input signal of any Simulink data type to the data type and scaling you specify for the Output data type parameter. The input can be any real- or complex-valued signal. If the input is real, the output is real. If the input is complex, the output is complex.

Note This block requires that you specify the data type and scaling for the conversion. If you want to inherit the data type or scaling from an input signal, use the Data Type Conversion Inherited block.

The Input and output to have equal parameter controls how the block handles the input. The possible values are Real World Value (RWV)and Stored Integer (SI):

Select Real World Value (RWV) to treat the input as V = SQ + B where S is the slope and B is the bias. V is used to produce Q = (V – B)/S, which is stored in the output. This value is the default.
Select Stored Integer (SI) to treat the input as a stored integer, Q. The value of Q is directly used to produce the output. In this mode, the input and output are identical except that the input is a raw integer lacking proper scaling information. Selecting Stored Integer might be useful in these cases:
- Generating code for a fixed-point processor
  The resulting code uses only integers and does not use floating-point operations.
- Partitioning your model based on hardware characteristics
  For example, part of your model might involve simulating hardware that produces integers as output.

Note When casting NaN values of type double to boolean, the Data Type Conversion block casts to boolean true.

Working with Fixed-Point Values Greater than 32 Bits

The MATLAB built-in integer data types are limited to 32 bits. If you want to output fixed-point numbers that range between 33 and 53 bits without loss of precision or range, you should break the number into pieces using the Gain block, and then output the pieces using the Data Type Conversion block to store the value inside a double.

Suppose that the original signal is an unsigned 128-bit value with default scaling. You can break this signal into four pieces using four parallel Gain blocks configured with the gain and output settings in the following table.

Piece	Gain	Output Data Type
1	`2^0`	`uint(32)` - Least significant 32 bits
2	`2^-32`	`uint(32)`
3	`2^-64`	`uint(32)`
4	`2^-96`	`uint(32)` - Most significant 32 bits

For each Gain block, you must also configure the Integer rounding mode parameter to Floor and clear the Saturate on integer overflow check box.

How Casting Works with Enumerated Signals

You can use a Data Type Conversion block to cast signal of an enumerated type to a signal of any numeric type, provided that the underlying integers of all enumerated values input to the block are within the range of the numeric type. Otherwise, an error occurs during simulation.

You can use a Data Type Conversion block to cast a signal of any integer type to a signal of an enumerated type, provided that every value input to the Data Type Conversion block is the underlying integer of some value in the enumerated type. Otherwise, an error occurs during simulation.

You cannot use a Data Type Conversion block to cast a non-integer numeric signal an enumerated signal. You cannot cast a complex signal to an enumerated signal regardless of the data types of its real and imaginary parts. See Using Enumerated Data for information about enumerated data types in Simulink.

When you generate code for a Data Type Conversion block that casts to an enumerated type, the code uses safe casting if you select the Saturate on integer overflow check box. If you clear this check box, the code does not use safe casting for enumerated types. See Enumerated Type Safe Casting for more information.

Data Type Support

The Data Type Conversion block handles any data type that Simulink supports, including fixed-point and enumerated data types.

For more information, see Data Types Supported by Simulink in the Simulink documentation.

Parameters and Dialog Box

Show data type assistant

Display the Data Type Assistant.

Settings

The Data Type Assistant helps you set the Output data type parameter.

See Specifying Block Output Data Types for more information.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Lock output data type setting against changes by the fixed-point tools

Select to lock the output data type setting of this block against changes by the Fixed-Point Tool and the Fixed-Point Advisor.

Settings

Default: Off

On: Locks the output data type setting for this block.
Off: Allows the Fixed-Point Tool and the Fixed-Point Advisor to change the output data type setting for this block.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Input and output to have equal

Specify which type of input and output should be equal.

Settings

Default: Real World Value (RWV)

Real World Value (RWV): Specifies the goal of making the Real World Value (RWV) of the input equal to the Real World Value (RWV) of the output.
Stored Integer (SI): Specifies the goal of making the Stored Integer (SI) value of the input equal to the Stored Integer (SI) value of the output.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Integer rounding mode

Specify the rounding mode for fixed-point operations.

Settings

Default: Floor

Ceiling: Rounds both positive and negative numbers toward positive infinity. Equivalent to the MATLAB ceil function.
Convergent: Rounds number to the nearest representable value. If a tie occurs, rounds to the nearest even integer. Equivalent to the Fixed-Point Toolbox™ convergent function.
Floor: Rounds both positive and negative numbers toward negative infinity. Equivalent to the MATLAB floor function.
Nearest: Rounds number to the nearest representable value. If a tie occurs, rounds toward positive infinity. Equivalent to the Fixed-Point Toolbox nearest function.
Round: Rounds number to the nearest representable value. If a tie occurs, rounds positive numbers toward positive infinity and rounds negative numbers toward negative infinity. Equivalent to the Fixed-Point Toolbox round function.
Simplest: Automatically chooses between round toward floor and round toward zero to generate rounding code that is as efficient as possible.
Zero: Rounds number toward zero. Equivalent to the MATLAB fix function.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Saturate on integer overflow

Specify whether overflows saturate.

Settings

Default: Off

On

Overflows saturate to either the minimum or maximum value that the data type can represent.

For example, an overflow associated with a signed 8-bit integer can saturate to -128 or 127.

Off

Overflows wrap to the appropriate value that is representable by the data type.

For example, the number 130 does not fit in a signed 8-bit integer and wraps to -126.

Tips

Consider selecting this check box when your model has possible overflow and you want explicit saturation protection in the generated code.
Consider clearing this check box when you want to optimize efficiency of your generated code.
Clearing this check box also helps you avoid overspecifying how a block handles out-of-range signals. For more information, see Checking for Signal Range Errors.
When you select this check box, saturation applies to every internal operation on the block, not just the output or result.
In general, the code generation process can detect when overflow is not possible. In this case, the code generator does not produce saturation code.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Sample time (-1 for inherited)

Enter the discrete interval between sample time hits or specify another appropriate sample time such as continuous or inherited.

Settings

Default: -1

By default, the block inherits its sample time based upon the context of the block within the model. To set a different sample time, enter a valid sample time based upon the table in Types of Sample Time.

See also How to Specify the Sample Time in the online documentation for more information.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Output minimum

Specify the minimum value that the block should output.

Settings

Default: []

The default value, [], is equivalent to -Inf.

Simulink software uses this value to perform:

Parameter range checking (see Checking Parameter Values) for some blocks
Simulation range checking (see Checking Signal Ranges)
Automatic scaling of fixed-point data types

Tip

This number must be a double scalar value.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Output maximum

Specify the maximum value that the block should output.

Settings

Default: []

The default value, [], is equivalent to Inf.

Simulink software uses this value to perform:

Parameter range checking (see Checking Parameter Values) for some blocks
Simulation range checking (see Checking Signal Ranges)
Automatic scaling of fixed-point data types

Tip

This number must be a double scalar value.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Output data type

Specify the output data type.

Settings

Default: Inherit: Inherit via back propagation

Inherit: Inherit via back propagation: Use data type of the driving block.
double: Output data type is double.
single: Output data type is single.
int8: Output data type is int8.
uint8: Output data type is uint8.
int16: Output data type is int16.
uint16: Output data type is uint16.
int32: Output data type is int32.
uint32: Output data type is uint32.
boolean: Output data type is boolean.
fixdt(1,16,0): Output data type is fixed point fixdt(1,16,0).
fixdt(1,16,2^0,0): Output data type is fixed point fixdt(1,16,2^0,0).
Enum: <class name>: Use an enumerated data type, for example, Enum: BasicColors.
<data type expression>: Use a data type object, for example, Simulink.NumericType.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Mode

Select the category of data to specify.

Settings

Default: Inherit

Inherit

Inheritance rules for data types. Selecting Inherit enables Inherit via back propagation.

Built in

Built-in data types. Selecting Built in enables a second menu/text box to the right. Select one of the following choices:

double (default)
single
int8
uint8
int16
uint16
int32
uint32
boolean

Fixed point

Fixed-point data types.

Enumerated

Enumerated data types. Selecting Enumerated enables a second menu/text box to the right, where you can enter the class name.

Expression

Expressions that evaluate to data types. Selecting Expression enables a second menu/text box to the right, where you can enter the expression.

Dependency

Clicking the Show data type assistant button enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Signedness

Specify whether you want the fixed-point data as signed or unsigned.

Settings

Default: Signed

Signed: Specify the fixed-point data as signed.
Unsigned: Specify the fixed-point data as unsigned.

Dependencies

Selecting Mode > Fixed point enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Word length

Specify the bit size of the word that holds the quantized integer.

Settings

Default: 16

Minimum: 0

Maximum: 32

Large word sizes represent large values with greater precision than small word sizes.

Dependencies

Selecting Mode > Fixed point enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Scaling

Specify the method for scaling your fixed-point data to avoid overflow conditions and minimize quantization errors.

Settings

Default: Binary point

Binary point: Specify binary point location.
Slope and bias: Enter slope and bias.

Dependencies

Selecting Mode > Fixed point enables this parameter.

Selecting Binary point enables:

Fraction length
Calculate Best-Precision Scaling

Selecting Slope and bias enables:

Slope
Bias
Calculate Best-Precision Scaling

Command-Line Information

See Block-Specific Parameters for the command-line information.

Fraction length

Specify fraction length for fixed-point data type.

Settings

Default: 0

Binary points can be positive or negative integers.

Dependencies

Selecting Scaling > Binary point enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Slope

Specify slope for the fixed-point data type.

Settings

Default: 2^0

Specify any positive real number.

Dependencies

Selecting Scaling > Slope and bias enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Bias

Specify bias for the fixed-point data type.

Settings

Default: 0

Specify any real number.

Dependencies

Selecting Scaling > Slope and bias enables this parameter.

Command-Line Information

See Block-Specific Parameters for the command-line information.

Examples

Real World Values Versus Stored Integers

The following model uses the Data Type Conversion block to explain the difference between a real-world value and a stored integer. Consider these two fixed-point block diagrams:

In the top block diagram, the Data Type Conversion block treats the input as a real-world value, and maps that value to an 8-bit signed generalized fixed-point data type with a scaling of 2^-2. When the value is then output from the Data Type Conversion1 block as a real-world value, the scaling and data type information is retained and the output value is 001111.00, or 15. When the value is output from the Data Type Conversion2 block as a stored integer, the scaling and data type information is not retained and the stored integer is interpreted as 00111100, or 60.

In the bottom block diagram, the Data Type Conversion3 block treats the input as a stored integer, and the data type and scaling information is not applied. When the value is then output from the Data Type Conversion4 block as a real-world value, the scaling and data type information is applied to the stored integer, and the output value is 000011.11, or 3.75. When the value is output from the Data Type Conversion5 block as a stored integer, you get back the original input value of 15.

Real World Values and Stored Integers in Summations

The following model shows how a summation operation applies to real-world values and stored integers, and how the generated code handles scaling information.

Note that the summation operation produces the correct result when the Data Type Conversion (2 or 5) block outputs a real-world value. This is because the specified scaling information is applied to the stored integer value. However, when the Data Type Conversion4 block outputs a stored integer value, then the summation operation produces an unexpected result due to the absence of scaling information.

If you generate code for the above model, then the code captures the appropriate scaling information. The code for the Sum block is shown below. The inputs to this block are tagged with the specified scaling information so that the necessary shifts are performed for the summation operation.

/* Sum Block: <Root>/Sum
   *
   *  y =  u0 + u1
   *
   * Input0  Data Type:  Fixed Point    S16  2^-2
   * Input1  Data Type:  Fixed Point    S16  2^-4
   * Output0 Data Type:  Fixed Point    S16  2^-5
   *
   * Round Mode: Floor
   * Saturation Mode: Wrap
   *
   */
  sum = ((in1) << 3);
  sum += ((in2) << 1);

Characteristics

Direct Feedthrough	Yes
Sample Time	Inherited from driving block
Scalar Expansion	N/A
Dimensionalized	Yes
Multidimensionalized	Yes
Zero-Crossing Detection	No

Data Type Conversion - Convert input signal to specified data type

Library

Description

Working with Fixed-Point Values Greater than 32 Bits

How Casting Works with Enumerated Signals

Data Type Support

Parameters and Dialog Box

Show data type assistant

Settings

Command-Line Information

Lock output data type setting against changes by the fixed-point tools

Settings

Command-Line Information

See Also

Input and output to have equal

Settings

Command-Line Information

Integer rounding mode

Settings

Command-Line Information

See Also

Saturate on integer overflow

Settings

Tips

Command-Line Information

Sample time (-1 for inherited)

Settings

Command-Line Information

Output minimum

Settings

Tip

Command-Line Information

Output maximum

Settings

Tip

Command-Line Information

Output data type

Settings

Command-Line Information

See Also

Mode

Settings

Dependency

Command-Line Information

See Also

Signedness

Settings

Dependencies

Command-Line Information

See Also

Word length

Settings

Dependencies

Command-Line Information

See Also

Scaling

Settings

Dependencies

Command-Line Information

See Also

Fraction length

Settings

Dependencies

Command-Line Information

See Also

Slope

Settings

Dependencies

Command-Line Information

See Also

Bias

Settings

Dependencies

Command-Line Information

See Also

Examples

Real World Values Versus Stored Integers

Real World Values and Stored Integers in Summations

Characteristics

See Also