The aim of this article is to provide guideline for disabling Trustzone on STM32U5.

1. Hardware and software setup

Nucleo MB1549-U5A5ZJT6Q1. Hardware and software setup
STM32CubeProgrammer

As you can see when connecting your board to STM32CubeProgrammer and checking the option bytes, TZEN is checked (TrustZone® enabled).

2. Disable TrustZone®

To disable TrustZone®, you have to:

Step 1: Connect Boot0 to VDD on your board:

This consists on connecting PH3 pin (CN11 pin 7) to VDD (CN11 pin 5).

Step 2: Connect your board with STM32CubeProgrammer in "hot plug" Mode.

Step 3: Switch RDP value in “readout protection” to level 1, then click on apply.

Step 4:

Switch RDP value to level 0
Uncheck the TZEN value in user configuration.

Step 5: Then click on apply to program the option bytes.

Step 6: Disconnect your board to STM32CubeProgrammer.
Step 7: Disconnect Boot0 to VDD.
Step 8: Connect again your board with STM32CubeProgrammer and make sure that TrustZone® is disabled(TZEN unchecked).

Reproduce this procedure faithfully otherwise the TrustZone® will not be disabled.