Lpc546xx: RESET during Boot ROM doesn't work

[giusloq]

At power up, LPC546xx MCU reads ISP bootstrap pins and, if one or more of them are low, Boot ROM is entered.

In this situation, I noticed that RESET pin doesn't work and the MCU keeps staying in the Boot ROM. The only solution to reset the MCU is a power cycle.

Is it normal?

[Miguel04]

Hi @giusloq 

I am Miguel.

I've been investigating your issue and I'm afraid that your board got bricked, however, there are methods to unbrick your board.

This method uses the SEGGER J-Link Lite Flash programming tool and the reset button. While running the SEGGER JFlashLite press the "Erase Chip" button and press the reset button. You will get more information on this post from Erich Styger.

Could you provide me more information, are you using a dev board?

Best Regards, Miguel.

[giusloq]

Hi Miguel, thank you for the answer.

However I think there was a misunderstanding. The MCU is not bricked, after a power cycle (and setting high all ISP pins) the application starts correctly.

The problem happens when the internal Boot ROM starts correctly because of some ISP pins sensed low. In this situation, the RESET pin appears not active so it's impossible to restart by pressing the RESET pushbutton. The only way to exit from internal bootloader (Boot ROM) is with a power cycle (cutting off the power supply).

Is it normal? I think the external signal on the RESET pin should be highest priority, even against internal bootloader.

[Miguel04]

Hi @giusloq 

Sorry for the misunderstanding. I believe the RESET behavior you are experiencing might be expected, concluding that the reset routing is working correctly but it is running the BootROM again immediately after the reset sequence. Could you please verify that the ISP pins are being restored after the reset to prevent it from continuously falling into ISP mode? Also, Does the reset button worked before or this always has been the normal behaviour since you got the board.

Miguel.