Access Block State Data

To model systems that switch between periodic or continuous time dynamics, use Simulink^® based states. Simulink based states are not supported in standalone Stateflow^® charts in MATLAB^®. For more information, see Simulink Subsystems as States.

You can read and write the state of blocks within your Simulink based states in transition actions of your Stateflow chart. You can read and write the state of blocks textually on the chart transitions or by using Simulink State Reader and State Writer blocks.

For example, the Stateflow chart in this example models a person moving through the stages of pole vaulting.

openExample("sf_pole_vault")

The first stage is the approach run of the vaulter, which is modeled by the Simulink based state Run_up. In the second stage, the vaulter plants the pole and takes off, which is modeled by the Simulink based state Take_off. The final stage happens when the vaulter clears the bar and releases the pole, which is modeled by the Simulink based state Fly.

The states Run_up and Fly are easier to model by using Cartesian coordinates. The state Take_off is easer to model by using polar coordinates. The Simulink functions InitTakeOff and InitFly are used to switch from one coordinate system to another. For more information on this chart, see Model a Pole Vaulter by Using Simulink Based States.

Textual Access

This subsystem is contained within the Simulink based state Run_up. For the transition from Run_up to Take_off to occur, the position of the pole vaulter along the x-axis, p(1), must be greater than -4.

By setting the State Name of the integrator block Position to 'p', you can textually access the state of this block from your Stateflow chart. To access the state of the integrator block in the transition condition, type [Run_up.p(1)> -4]. When this condition becomes true, the transition is taken and the active state becomes Take_off.

In the Symbols pane, you can see that the state p appears under the state Run_up.

Graphical Access

Stateflow uses State Reader and State Writer blocks to connect the subsystems within a Simulink based state to other Simulink subsystems in your model. State Reader and State Writer blocks display the name of the state owner block that they are connected to. Conversely, the state owner block displays a tag indicating a link to a State Reader or a State Writer block. If you click the label above the tag, a list opens with a link for navigating to the State Writer block.

Connect a State Reader Block to an Owner Block

The following subsystem is contained within the Simulink function InitTakeOff. The function uses State Reader blocks to connect to the state Run_up and reads p and v. The function then converts the Cartesian values for the position of the pole vaulter and velocity into polar coordinates, r and theta and rdot and theta_dot, respectively. These polar coordinates are then accessed by using state owner blocks in the state Take_off.

When the transition action occurs, the State Reader blocks in InitTakeOff read the state of their state owner blocks. Once the Simulink function finishes executing, the State Writer blocks write to the state owner blocks in the Simulink based state Take_off.

To connect a State Reader or a State Writer block to an owner block within a Simulink subsystem:

1. To open the properties, double-click the State Reader.

2. In the State Owner Selector Tree, navigate to the block that you want to be the state owner block. In this example, by choosing Position, you connect the State Reader block to the integrator Position in the state Run_up.

   

3. By connecting the State Reader block to the Position integrator block, this Simulink function can use the state of the integrator Position to execute.

Related Topics

• Simulink Subsystems as States
• State Reader (Simulink)
• State Writer (Simulink)