USB communication between PICs

The USB protocol identifies two sides of a communication: the host and the device. The host controls the communication and does more work than the device. Generally the host is a computer, and the PIC is the device. However, if you configure a PIC as a host you can do certain new things:

• Plug in a flash drive USB device to use as storage.
• Configure another PIC as a USB device and use USB to communicate between them.

The Microchip USB Framework includes an embedded host stack that provides code for running a PIC as a USB host. The PIC 18f4550 is not able to run as an embedded host: to run the embedded host stack requires a 16-bit or 32-bit PIC. The 4550 is a mere 8-bit chip.