LPC55S0 Default/Reset state of DEFAULT_ISP_BITS in the CMPA

[Ash17]

What is the default/reset state of the DEFAULT_ISP_BITS in the CMPA of the LPC55S06JHI48 MCU? I am trying to confirm if the MCU will automatically be able to detect that the program image is coming on UART when no image is present on internal flash. The goal is to have the MCU be able to be programmed by UART without any HW pin setting or SW configuration.

So far, I have not found this information for the LPC550x/S0x family. But I found the AN13543 application note for the LPC553x/LPC55S3x which explains the default state of these bits on page 3 solely for that MCU family.

[Ash17]

Raul, thank you for the response. I just wanted to confirm the default DEFAULT_ISP_MODE would be Auto ISP since that wasn't clear from the user manual even in section 6. One last follow-up question I have is, is the flow chart for ISP0 (PIO0_5 pin) is detected as HIGH with no image loaded in flash, as shown in the attached image? I have shown the flow of this case in red arrows to confirm.

[RaRo · Accepted solution]

Hello @Ash17,

In passive boot mode (ISP pin not asserted), if the internal flash image is deemed invalid, and you do not have SPI_RECOVERY_BOOT_EN (bits 3:0) in protected flash SPI_FLASH_CFG (0x3E404) enabled to SPI flash recovery. Then the flow would be as you mentioned.

Kind regards, Raul.

[Ash17]

I understand now. Thank you for the quick answer. 

[RaRo]

Hello @Ash17,

Could you please take a look at the LPC55S0x/LPC550x User manual. Chapter 6: LPC55S0x/LPC550x Boot ROM?

There you could look the LPC55S0x/LPC550x boot flow chart which shows the boot process.

Also, is mentioned that the LPC55S0x/LPC550x will read the status of the ISP pins to determine boot source. Then if the ISP0 (PIO0_5 pin) is detected as HIGH: The LPC55S0x/LPC550x will look for valid image in the internal flash, if no valid image is found, the LPC55S0x/LPC550x will enter ISP boot mode based on DEFAULT_ISP_MODE bits. Finally, the default DEFAULT_ISP_MODE would be Auto ISP.

Kind regards, Raul.