Block Sample Times :: How Simulink Works (Using Simulink)

Using Simulink

Block Sample Times

Every Simulink block is considered to have a sample time, even continuous blocks (e.g., blocks that define continuous states, such as the Integrator block) and blocks that do not define states, such as the Gain block. Discrete blocks allows you to specify their sample times via a Sample Time parameter. Continuous blocks are considered to have an infinitesimal sample time called a continuous sample time. A block that is neither discrete or continuous is said to have an implicit sample time that it inherits from its inputs. The implicit sample time is continuous if any of the block's inputs are continuous. Otherwise, the implicit sample time is discrete. An implicit discrete sample time is equal to the shortest input sample time if all the input sample times are integer multiples of the shortest time. Otherwise, the implicit sample time is equal to the fundamental sample time of the inputs, where the fundamental sample time of a set of sample times is defined as the greatest integer divisor of the set of sample times.

Simulink can optionally color code a block diagram to indicate the sample times of the blocks it contains, e.g., black (continuous), magenta (constant), yellow (hybrid), red (fastest discrete), and so on. See Mixed Continuous and Discrete Systems for more information.

Custom Blocks

Simulink allows you to create libraries of custom blocks that you can then use in your models. You can create a custom block either graphically or programmatically. To create a custom block graphically, you draw a block diagram representing the block's behavior, wrap this diagram in an instance of the Simulink Subsystem block, and provide the block with a parameter dialog, using the Simulink block mask facility. To create a block programmatically, you create an M-file or a MEX-file that contains the block's system functions (see the Writing S-Functions). The resulting file is called an S-function. You then associate the S-function with instances of the Simulink S-Function block in your model. You can add a parameter dialog to your S-Function block by wrapping it in a Subsystem block and adding the parameter dialog to the Subsystem block.

Tunable Parameters Systems and Subsystems