The PIC18C601 and PIC18C801 microcontrollers are the first members of Microchip’s PIC18 family with no on-chip program memory. They offer the PIC18 archi- tecture, with the ability to use different types and sizes of external program memory (up to 2 Mbyte) to exactly fit most applications. In modern embedded applications, where features and functionality are constantly evolving, FLASH memory is an ideal choice for external program memory. Field upgradability is almost always desirable in these sys- tems, too. Most commonly available FLASH devices, however, disable read access while being programmed or erased. They also require special command sequences for programming, and have longer erase and write times than read times. As a result, systems using FLASH technology require either a second mem- ory device, or a microcontroller with built-in memory space, in order to implement field reprogrammability. PIC18C601/801 controllers do this by allowing part of on-chip data memory to be reconfigured as program memory.M AN819 Implementing Bootloader Firmware for the PIC18C601/801 ROMless Microcontrollers This application note discusses the general design Authors: Gaurang Kavaiya and Nilesh Rajbharti requirements for bootloader firmware in a ROMless Microchip Technology Inc. controller system. To illustrate the key points, a fully- featured reference design, with an interface to external host soft……