FRDM-MCXA156 Brown out setting or Low voltage setting

[Puneeth1]

Hi everyone,

I’m looking for a simple example program that demonstrates brownout detection and handling in a FRDM-MCXA156 board.

I already understand how brownout works conceptually, but I would like to see:

• A practical code example

• How brownout detection is configured

• How the system reacts when voltage drops

• How to safely recover after brownout reset

If possible, please share a minimal working example in c.

Thanks in advance!

[Celeste_Liu]

Hello @Puneeth1 ,

Thanks for your post. You can configure SYS_LVDE/CORE_LVDE/BGMODE bits in ACTIVE_CFG/LP_CFG registers.

I recommend you refer to our SDK demo power_mode_switch. You can download SDK from Select Board | MCUXpresso SDK Builder.

In this demo, you can see how to use SPC driver API to enable LVD.

power_mode_switch.c:

from line 166:

/* Enable LVDs and HVDs in active mode. */

SPC_EnableActiveModeCoreLowVoltageDetect(APP_SPC, true);

SPC_EnableActiveModeSystemHighVoltageDetect(APP_SPC, true);

SPC_EnableActiveModeSystemLowVoltageDetect(APP_SPC, true);

/* Disable LVDs and HVDs in low power mode to save power. */

SPC_EnableLowPowerModeCoreLowVoltageDetect(APP_SPC, false);

SPC_EnableLowPowerModeSystemHighVoltageDetect(APP_SPC, false);

SPC_EnableLowPowerModeSystemLowVoltageDetect(APP_SPC, false);

In fact, the voltage detect monitors enable by default and keeps the MCU in reset until the supply voltage rises above the LVD rising threshold. Whenever the voltage detect monitors are enabled, they trigger a reset condition if the supply voltage is outside the voltage detect trip point.
SRS[VD] becomes 1 on voltage detect condition. The voltage detect monitors assert a cold reset(reset the debug logic and mode control logic) in all power domains.

Hope it helps.

BR

Celeste

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[Puneeth1]

Hi @Celeste_Liu,

Thank you for your response! I appreciate the explanation about the LVD reset behavior and the pointer to the power_mode_switch SDK demo.

However, my actual requirement is slightly different from what was covered. I need to configure the LVD to trigger an interrupt (ISR) instead of (or in addition to) a reset, so that my application can:

1. Detect a low voltage condition at runtime
2. Handle it gracefully inside an ISR (e.g., save state, log the event, or initiate a controlled shutdown)
3. Resume or recover without necessarily triggering a full cold reset

Specifically, I would like to know:
- How to configure the SPC/LVD to generate an interrupt instead of (or before) asserting a reset
- Which NVIC interrupt vector corresponds to the LVD event on MCXA156/155
- How to write and register the ISR to capture the LVD event
- How to clear the LVD interrupt flag inside the ISR

A minimal working C code example demonstrating this interrupt-driven LVD detection on the FRDM-MCXA156 would be extremely helpful.

Thank you in advance!

BR,
Puneeth

[Celeste_Liu]

Hello @Puneeth1 .

On MCXA156, the Low-Voltage Detect (LVD) function is classified as a power-on reset source. When supply voltage drops below the threshold, it immediately triggers a cold reset. As a result:

• No NVIC interrupt is generated for LVD.
• There is no LVD interrupt flag to clear.
• After the device restarts, you can only perform post-mortem diagnosis by reading the CMC reset status registers to determine whether the reset was caused by LVD (e.g., SRS[VD] / SSRS[VD]).

In summary, the four requested “LVD interrupt” items are not supported on MCXA156:

1. Generate an interrupt from SPC/LVD: Not supported (LVD follows the cold-reset path only).
2. Corresponding NVIC vector: Not available.
3. Write/register an LVD ISR: Not applicable.
4. Clear an LVD flag inside an ISR: Not applicable (diagnose after reset by reading SRS/SSRS).

Therefore your requirements cannot be fulfilled using the LVD mechanism.

BR

Celeste