Configure Blocks with Fixed-Point Parameters - MATLAB & Simulink (original) (raw)

Main Content

Certain Simulink® blocks allow you to specify fixed-point numbers as the values of parameters used to compute the block's output, for example, theGain parameter of a Gain block.

Note

S-functions and the Stateflow® Chart block do not support fixed-point parameters.

You can specify a fixed-point parameter value either directly by setting the value of the parameter to an expression that evaluates to a fi object, or indirectly by setting the value of the parameter to an expression that refers to a fixed-point Simulink.Parameter object.

Note

Simulating or performing data type override on a model with fi objects requires a Fixed-Point Designer™ software license. See Sharing Fixed-Point Models for more information.

Specify Fixed-Point Values Directly

You can specify fixed-point values for block parameters using fi objects. In the block dialog's parameter field, simply enter the name of a fi object or an expression that includes the fi constructor function.

For example, entering the expression

as the Constant value parameter for theConstant block specifies a signed fixed-point value of 3.3, with a word length of 8 bits and a fraction length of 3 bits.

Specify Fixed-Point Values via Parameter Objects

You can specify fixed-point parameter objects for block parameters using instances of the Simulink.Parameter class. To create a fixed-point parameter object, either specify a fi object as the parameter object's Value property, or specify the relevant fixed-point data type for the parameter object's DataType property.

For example, suppose that you want to create a fixed-point constant in your model. You could do this using a fixed-point parameter object and a Constant block as follows:

  1. Enter the following command at the MATLAB® prompt to create an instance of the Simulink.Parameter class:
    my_fixpt_param = Simulink.Parameter
  2. Specify either the name of a fi object or an expression that includes the fi constructor function as the parameter object's Value property:
    my_fixpt_param.Value = fi(3.3,1,8,3)
    Alternatively, you can set the parameter object's Value and DataType properties separately. In this case, specify the relevant fixed-point data type using a Simulink.AliasType object, a Simulink.NumericType object, or a fixdt expression. For example, the following commands independently set the parameter object's value and data type, using a fixdt expression as theDataType:
    my_fixpt_param.Value = 3.3;
    my_fixpt_param.DataType = 'fixdt(1,8,2^-3,0)'
  3. Specify the parameter object as the value of a block's parameter. For example, my_fixpt_param specifies the Constant value parameter for the Constant block in the following model:

    The Constant block outputs a signed fixed-point value of 3.3, with a word length of 8 bits and a fraction length of 3 bits.

See Also

Topics