Reset B Pin disconnected

[HeebeomPark]

Software assumption
Application software activates pull-down on RESET_b pad before running the safety application.

Question#1) To activate the pull-down on RESET_b, the following shall be done?

 

1. Identify the MSCR Register for RESET_B:

   • RESET_B is typically mapped to PTA5, which corresponds to SIUL2_MSCR5.

2. Set the Pull Enable and Pull Select Bits:

   • PUE (bit 13) = 1 → Enables internal pull resistor.
   • PUS (bit 11) = 0 → Selects pull-down (when PUE is enabled).

3. Optional: Enable Input Buffer (if needed for monitoring):

   • IBE (bit 19) = 1

4. Optional: Disable Output Buffer (if not used):

   • OBE (bit 21) = 0

Rationale
Ensures that the chip enters a chip safe state if the RESET_b pin gets disconnected.

Recommendation
—

Question#2)

In order to detect the Reset_b pin is disconnected,  one of the following shall be done?

Option 1: Use MC_RGM.FES[F_EXR]

• Monitor this flag to see if RESET_B was unexpectedly asserted.
• If it is never set, and you expect external resets, it may indicate a disconnection.

Option 2: Use a GPIO for Redundancy

• If possible, connect RESET_B to a GPIO input on the MCU or another monitoring device.
• Periodically sample the pin level to verify it is high during normal operation.
• This allows software to detect if the pin is floating or stuck low.

Option 3: External Watchdog or SBC Monitoring

• Many systems use an external Safety Power Management IC (PMIC) or SBC that monitors RESET_B.
• These devices can detect if RESET_B is not behaving as expected and report faults.

[john_floros]

Hello,

1. I beleive to acivate an pull-down on the reset pin this would have to be done externally.  This cannot be done using the application and manipulation of the MSCR register.  See the following excerpt from the RM:

2. For the detection method of a disconnected reset pin:

Option 1: My opinion is that this option is not a reliable method for detecting a disconnected reset pin.

Option 2: My opinion is this is a good second option but still not ideal since the GPIO pin may still be connected while the RESET_b pin is not.

Option 3: This is, in my view the best option and is how our safety recommendations are usually implemented.

You could also implement a combination of all three options.

Regards,

John