FRDM-MCXA156 Debug Connection Failure — “Wire Ack Fault” / “Could not connect to core”

[udaysinghg70]

Summary

I am working with an NXP FRDM-MCXA156 Development Board using MCUXpresso IDE and the onboard MCU-Link (LinkServer) debugger.

I am unable to erase, flash, or debug the target MCU after attempting to enter Serial Downloader (ISP) mode.

The debugger detects the onboard probe correctly, but fails to connect to the target MCU core.

Board / Software Information

Board: NXP FRDM-MCXA156 Development Board
MCU: MCXA156
IDE: MCUXpresso IDE Version 25.6.136
Debugger backend: LinkServer RedlinkMulti Driver v25.6
Probe: Onboard MCU-Link
OS: Windows
SDK example used: hello_world

Problem Description

Initially, the board was working normally.

I wanted to put the board into Serial Downloader mode (ISP mode), so I followed the board procedure:

1. Hold SW3 (ISP)
2. Press and release SW1 (RESET)
3. Release SW3

After doing this, I attempted to use the debugger again from MCUXpresso.

Since then:

• Debug fails
• Erase fails
• Flash fails

The onboard MCU-Link is detected, but the target core is not accessible.

Error 1: Wire Ack Fault

When trying to connect:

Unable to connect wire for probe index 1.

Error: Wire Ack Fault - target connected?

Unable to connect wire for probe index 1.

Error: Wire Ack Fault - target connected?

Stack trace:

Error: Wire Ack Fault - target connected?

at com.nxp.mcuxpresso.core.debug.support.linkserver.redlink.client.RedlinkServerClient.checkServerReply(...)

at com.nxp.mcuxpresso.core.debug.support.linkserver.redlink.client.RedlinkServerClient.wireConnect(...)

...

Error 2: Erase Failure

When executing erase:

Executing flash operation 'Erase' (Erase flash)

Checking MCU info...

Scanning for targets...

Executing flash action...

LinkServer output:

LinkServer RedlinkMulti Driver v25.6

Found chip XML file ... MCXA156.xml

Connecting to probe 1 core 0

Ee(42). Could not connect to core.

Retrying...

Server OK but no connection to probe 1 core 0

Ee(42). Could not connect to core.

Failed on connect: Ee(42). Could not connect to core.

No connection to chip's debug port

Target Operation Failed

Unable to perform operation!

Command failed with exit code 1

What I Have Tried

1. Normal reset

• Released ISP button
• Pressed reset
• Retried debug

Result: Failed

1. Power cycle

• Unplugged USB
• Reconnected board

Result: Failed

1. Erase via MCUXpresso

Used Flash Tool → Erase

Result:

No connection to chip's debug port

1. Verified probe detection

MCU-Link is detected properly by MCUXpresso.

So the probe itself appears functional.

Questions

1. After entering ISP mode, can the MCXA156 remain in a state where SWD becomes unavailable?
2. Is it possible that my firmware disabled SWD pins or locked debug access?
3. What is the recommended recovery path for FRDM-MCXA156?

• Connect under reset?
• Mass erase via MCU Boot Utility?
• Full recovery of MCU-Link firmware?

1. Can entering Serial Downloader mode affect later SWD debugging if not exited correctly?

Additional Information

Board manual indicates:

• SW3 = ISP button (target bootloader entry)
• SW1 = Reset

I am using the onboard debugger, not an external probe.

Any recovery procedure or known issue with MCXA156 debug lock / ISP interaction would be helpful.

[luis_maravilla · Accepted solution]

Hello

Could you help us sharing your jumper configuration:

JP5: ISP_EN_SWD_ACT Shorted

This will force MCU-Link to ISP mode, to reprogram the MCU-Link internal flash

JP6:VCOM_DIS Open [VCOM Enable]

JP7: SWD_DIS Open [SWD Enable]

JP8: SWD_CLK Shorted [SWD Clock Enable]

JP2: MCU_DIGITAL_POW Shorted [VDD_MCU Supply]

This information is from [FRDM-MCXA156 Board User Manual] Chapter 1.6 Table 4

Could you help us share how the attached probe is shown in MCUXpresso?

Could you help us try enter ISP via JP5 to force ISP mode; Then try to do mass erase

This is the ISP commands for Mass erase:

First recognize the device with success response

>blhost -p COMxx,115200 -- get-property 1

Then Mass erase with success response:

>blhost -p COMxx,115200 -- flash-erase-all

In the ISP path you can enter ROP States where the debug is disabled or have reduced commands.

Please refer to MCXA156 Reference Manual Chapter 20.2.5 Figure 29 page 732.

And Chapter 20.3.2 Lifecycle State transition

Best Regards, Luis

[udaysinghg70]

Hello Luis,

Thank you for the detailed guidance.

The solution worked and the issue has been resolved successfully.

I entered ISP mode by forcing ISP through JP5 and then performed the mass erase using the following commands:

blhost -p COMxx,115200 -- get-property 1
blhost -p COMxx,115200 -- flash-erase-all

After the mass erase completed successfully, the probe recovered and is now functioning normally.

Thank you again for your support and the detailed explanation regarding the ISP path and lifecycle states.

Best Regards, Uday