I suppose you will be wiring a Web Cam to the PIC.
The USB currently has 3 different speeds: Low Speed :1.5Mbps, Full Speed: 12Mbps and High Speed 480Mbps.
As far as the wiring is considered you can take a USB Connector, attach one end to the web cam, and at the other end separate out the wires. You should see the foll wires:
Green Color --- + Data
White------ -Data
Red ------ Vcc
Black ---- Ground
+Data and –Data form a differential system of data (to cancel the noise). Now you build a scheme so that you get your original data back ie Pulses wrt gnd. Remember that the data is in NRI-Z format.
The next part is a bit trick…You need to follow the USB protocol. Now USB uses packets for transferring of data. Every exchange is a 3 tier process…
1. Token Packet—Here the address of your device is given
2. Data Packet----Here the Actual Data is sent
3. Handshake Packet—Here the handshaking is done to complete the exchange
Note that both token and data packet are internally divided into sub field comprising of sync, packet identification & error check.
So now you have to choose your speed at both ends, assume your WebCam transferrs data at 9600 bps so in your MCU set the baud rate at 9600 bps and then use a logic scheme to seperate out each packet and in turn each sub packet . Then you can ultimately sort out your data.
Check out
https://www.usb.org for more details.