Hello @jamie3
1)USB DFU mode, refer to:
https://community.nxp.com/t5/LPC-Microcontrollers-Knowledge/Use-blhost-to-program-erase-LPC54-S-0xx-...
2) UART ISP command. below is method from our SE team:
In order to program the SPIFI flash, the flashloader has to be placed in to the RAM and execute from there.
The entire procedure can be described as follows:
- Put the device into ISP mode
- Synchronize USART ISP interface
- Write the content of flashloader.bin to SRAMX (0x0000_0000)
- Use Go command to start the execution of the flashloader
- Communicate with the flashloader using blhost
For step 2-4, please refer to the attached archive, which contains a simple python script to download and execute the flashloader using the ISP commands. Please also note this script is for reference only and comes without waranty, thus should not be used in production.
In order to use the script, the following steps should be performed:
- Extract the contents of the archive to a directory
- Prepare Python3 environment
- Open a command line window, navigate to the extracted directory, and execute: pip install -r requirements.txt
- Connect the board's ISP UART to the computer and put the device into ISP mode
- Modify the connection parameters located in pyisp.py, such as port and baud rate (see below).
- In the same directory, execute: python pyisp.py
Parameter settings:

If everything has been set up correctly, the following output can be observed in the commandline window:

The flashloader should be running by now, and with blhost, we can communicate with the flashloader.
The source code of the flashloader can be obtained from SDK bootloader_examples/flashloader
Please refer to "Getting Started with LPC540xx/LPC54S0xx Flashloader User's Guide" for further configuration of the SPIFI flash. Note the connection mode should be UART instead of USB:


The SPIFI configuration word should be placed outside of the reserved region:



Then the user should be able to erase or program the external flash memory:

BR
Alice