Bus signals not visible in deeply nested subsystems in Simulink

Hello everyone,

I am working on a MATLAB/Simulink model that consists of multiple nested subsystems. At the top (main) model level, I have a Bus Creator that bundles several signals into a bus, and this bus is routed to multiple subsystems.

At higher-level subsystems, I am able to access the bus signals correctly using a Bus Selector block. However, when I try to access the same bus inside deeper (interior) subsystems, the Bus Selector is not able to detect or extract any signals from the bus.

So far, I’ve observed that:

• The Bus Selector works correctly up to 2 levels of subsystem depth
• Beyond that depth, the bus appears to be “empty” or unavailable in the interior subsystems
• The bus connection itself is still present, but none of the individual signals show up in the Bus Selector

I would like to understand:

1. Why does this limitation occur when accessing bus signals in deeper nested subsystems?
2. Is this related to bus scoping, virtual vs non-virtual buses, or signal hierarchy?
3. What is the recommended way to pass and access bus signals reliably across multiple subsystem levels?

Any guidance, best practices, or example models would be greatly appreciated.

Thank you in advance!

[Paul]

FWIW, I tried in 2024a and the Bus Selector worked as expected four subsystems down from the top level of the model. The bus contained two signals and model has ordinary, nested Subsystem blocks.

Answer 1

[Izhar]

Define your bus once using a Bus Object and explicitly apply it at every subsystem interface.