Obtaining Parameters from Prototypes in TestStand

When calling a subsequence, TestStand normally uses the parameter list defined in that subsequence. However, there are situations where you need to import parameter definitions from another sequence—for example, when you want multiple Sequence Call steps to follow the same parameter structure, or when you want to dynamically call different subsequences that share a similar prototype.

The Load Prototype feature allows TestStand to automatically update a Sequence Call step’s parameters based on the prototype of another sequence.

When to Use Load Prototype

Use Load Prototype when:

• You want the calling step to match the parameter list of a different sequence.
• You have several subsequences with similar interfaces and want to keep parameter lists in sync.
• You are dynamically selecting subsequences at runtime and want the Sequence Call step to adapt to the chosen target’s parameters.
• You want to avoid manually adding or modifying parameters when using shared or reusable subsequences.

This feature helps maintain consistency and prevents errors caused by mismatched parameter lists.

Loading a Prototype into a Sequence Call Step

To load the parameter definition from another sequence:

1. Select the Sequence Call step you want to update.
2. In the Step Settings pane, open the Module tab.
3. Uncheck Use Prototype of a Sequence if it is enabled. This option is disabled if you check Specify By Expression.
4. Click Load Prototype.
5. Select the sequence whose prototype you want to use.

After selecting a sequence, TestStand updates the parameter list of the Sequence Call step based on the chosen sequence’s prototype.

What Happens When You Load a Prototype

When you load a prototype, TestStand compares the prototype of the selected sequence with the current Sequence Call’s parameters:

• If the target sequence includes additional parameters that are not present in the Sequence Call, TestStand adds those parameters dynamically at run time.
• Existing parameters that already match remain unchanged.
• Parameters are not removed—only added when needed.

This ensures the Sequence Call step includes all required parameters but does not unexpectedly delete or modify mappings you already configured.

To learn more about this use case, follow the Calling Sequences Dynamically tutorial of the Fundamentals >> Getting Started with TestStand section of the TestSTand Help.

This feature is especially useful when a Sequence Call uses an expression to determine which subsequence to call at runtime. In that case:

• Multiple subsequences may share the same interface.
• You want the parameter list to remain aligned across all of them.
• Using Load Prototype ensures the Sequence Call step stays compatible with any subsequence your expression evaluates to.

This reduces maintenance effort and minimizes errors caused by mismatched parameter definitions.