Working with Data Type Expression - Working with Data Type Expression - 2026.1 English - UG1483

Vitis Model Composer lets you specify data types as an expression. Currently the following HLS library blocks support data type expression:

• Constant
• Data Type Conversion
• Gain
• Look-Up Table
• Reinterpret

To specify a data type expression, open one of the block types that support it, and edit the data type and value. The following example shows a data type expression being defined for the Constant block. The example specifies the Output data type as an expression, and specifies a string to indicate the data type value, in this case uint32.

You can specify the data type value as a string representing any of the supported data types shown in the Model Composer Data Types table. Refer to Working with Data Types for supported data types. The exception to this rule is for fixed point data types. The fixed string does not specify these. The display format discussed in Working with Fixed-Point Data Types defines fixed-point data types (for example, x_sfix16_En8).

The benefit of defining data types as expressions is the ability to programmatically determine the data type value using a variable from the model. For instance, if you define a variable from the MATLAB® command line:

>> InputDataType = 'x_ufix8_En7';

You can use the variable in defining the data type expression.

Figure 2. Variable Data Type

You can specify variables from the MATLAB command line, or define variables within the model by selecting Modeling > Design > Model Explorer menu command, or simply pressing Ctrl+H. From the Model Explorer you can create, edit, and manage variables that the model or a block uses.