The following document is interesting. They have integrated a 18F4550on t=
he Explorer 16 Demo board.
http://ww1.microchip.com/downloads/en/DeviceDoc/51589a.pdfExplorer 16 Dev=
elopment Board User's Guide
It is using the PICkit 2 PC application to update the firmware.
Regards,Xiaofan
**************************************************************4.2.5 USB C=
onnectivityThe Explorer 16 board includes a PIC18LF4550 USB microcontroll=
er, which providesboth USB connectivity and support for protocol translat=
ion. The PIC18LF4550 ishard-wired to the PIC24/dsPIC33F devices to provid=
e three types of connectivity:=95 SPI=99 of PIC18LF4550 to SPI1 of PIC24/=
dsPIC33F=95 I/O pins of PIC18LF4550 to ICSP=99 pins of PIC24/dsPIC33F=95 =
I/O pins of PIC18LF4550 to JTAG pins of PIC24/dsPIC33FThe type of connect=
ivity depends on the firmware installed on thePIC18LF4550. At thetime of =
initial release, the PIC18LF4550 is loaded with USB bootloaderfirmware, w=
hichpermits easy upgrades of connectivity firmware over the USB.Installin=
g this firmwareis described in Appendix B. "Updating the USB Connectivity=
 Firmware".PIC24 and dsPIC33F devices both have some 5V tolerant input pi=
ns. If a5V tolerantinput is connected to the PIC18LF4550, protection diod=
es on the PIC18LF4550device's port pins will limit inputs to VDD. For mor=
e information onwhich pins of the16-bit devices are 5V tolerant, refer to=
 the appropriate device data sheet.

********************************************************Appendix B. Updat=
ing the USB Connectivity Firmware
B.1 INTRODUCTIONThe USB subsystem of the Explorer 16 Development Board is=
 preprogrammed withUSB bootloader firmware. This provides an easy method =
for upgrading thePIC18LF4550 firmware to support ICSP, JTAG and SPI conne=
ctivity to PIC24 anddsPIC33F devices.This chapter describes how to upgrad=
e the PIC18LF4550 device's firmware with thePICkit 2 software. The same p=
rocess can be used to upgrade the PIC18LF4550device's firmware when updat=
es and new firmware packages become available.
B.2 UPDATING THE PICkit 2 MICROCONTROLLER PROGRAMMERBefore beginning, it =
will be necessary to obtain and install thePICkit 2 programmersoftware. C=
omplete instructions for installing and using the programmer softwareappl=
ication is provided in the PICkit=99 2 Microcontroller Programmer User's =
Guide(DS51553). The programmer and user's guide, as well as the latest ve=
rsion of thePICkit 2 operating system firmware, are available from the Mi=
crochip corporateweb site, www.microchip.com.
--=20
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