In most LPC2000 devices, the primary bootloader is the firmware which resides in the Boot Block and is executed every time the part is powered on or reset. The secondary bootloader in this document refers to a user-defined application that provides the user with an option to update the code or execute the previously programmed code.
In Application Programming (IAP executes erase and write operations on the on-chip flash memory, as directed by the end-user application code.
Code update is a typical application of IAP. This document describes four secondary bootloaders using different interfaces (UART using the 1K XMODEM protocol, SD/MMC using a FAT file system, I2C interfaced to EEPROM and CAN).