Download: BCM2835 PDF Datasheet
The file is in a zip format to save download times.
The Broadcom BCM2835 System on Chip (SoC) is located below the Samsung memory chip as shown in the diagram above. By stacking the memory chip above the processor chip, it saves PCB space.
The datasheet documents the use of all the input output ports such as the GPIO pins, SPI, PWM, and USB.