As the family Encore II program using the Bootloader.
What is the circuitry necessary and the program for the PC.
You don't need any extra circuitry in your USB device to support Boodtloader.
You should have some way to enter bootloader mode.( switch press or through set report feature )
Please refer to this App note for more details:
Thanks & Regards,
here is demo video for bootloader in enCoRe II