Hello.
I am using a PIC 18f2550 to drive a 128x64 graphic lcd display.
The PIC receives data and is power from the USB port.

The PIC uses the Microchip HID bootloader for the firmware upgrades.

Some units stopped working and I can't figure out why. The PIC is not
detected by the USB bus and doesn't display the usual startup screen on the
display.

I tried to enable the usb bootloader like if I had to upgrade the firmware
but even the bootloader is not detected by the usb bus.
The only thing that worked was to using the PicKit to program the PIC with
the bootloader and than load the application again.

I can't figure out how the code was deleted from pic.
I have half idea but I don't know if it makes sense. The commands from the
PC are arrays of 35 bytes. this commands are stored in the PIC in a buffer
containing up to 7 commands (so it is a 35x7 byte array).

The application on the PIC consumes the buffer when a command is extracted
and executed.
It could be possible I make some mistakes when I manipulate the buffer and
write memory locations I am not supposed to.

But I don't think I can esare the chip only writing the wrong memory
location, do I?

I have also considered that the problem could be the power from the USB
port, which may not be "clean" or stable.
But I have other devices power by the USB port and never had a problem (the
PIC is different though).

I was wondering if anybody has an idea of what happened.

Thanks
Cristiano
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