LPC55S6x/LPC55S2x/LPC552x User manual UM11126 says USB0 is also possible for ISP mode.
I tried this with LPCXpresso55S69:
connected USB port of LPCXpresso with Windows-PC
connected to USB1 USB Device 1fc9:0021 appeared, if poweron with ISP0 pulled down.
connected to USB0 no USB Device was recognized by Windows with ISP0 pulled down.
What do I have to do, to test the USB-Bootloader option at USB Port0?
I want to transfer this info to use bootloader at USB0 with LPC55s28 for mass production.
see also: How to use LPC55S28 Bootloader
Edit: Also tried to pull down P0_4 and P0_6; with P0_5 pulled up. like in Use blhost to program/erase LPC540xxM/LPC54S0xxM flash : Also no USB0 activity.