Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 849

Chapter 31
Universal Serial Bus (USB)
The universal serial bus (USB) controller allows the MPC885 to communicate with other devices via a
USB connection. This chapter describes the MPC885's USB controller, including basic operation, the
parameter RAM, and registers. It also provides programming examples for initializing host mode and
function mode of the USB controller.
31.1 USB Integration in the MPC885
The USB peripheral replaces SCC1 of the MPC885.
31.2 Overview
The universal serial bus (USB) is an industry-standard extension to the PC architecture. The USB
controller on the MPC885 supports data exchange between a wide range of simultaneously accessible
peripherals. Attached peripherals share USB bandwidth through a host-scheduled, token-based protocol.
The USB physical interconnect is a tiered-star topology, and the center of each star is a hub. Each wire
segment is a point-to-point connection between the host and a hub or function, or a hub connected to
another hub or a function. The USB transfers signal and power over a four-wire cable, and the signalling
occurs over two wires and point-to-point segments. The USB full speed signalling bit rate is 12 Mbps.
Also, a limited capability low speed signalling mode is defined at 1.5 Mbps. Refer to the USB
Specification Revision 1.1 and Revision 2.0 for further details. They can be downloaded from
http://www.usb.org.
The MPC885 USB controller consists of a transmitter module, receiver module, and two protocol state
machines. The protocol state machines control the receiver and transmitter modules. One state machine
implements the function state diagram and the other implements the host state diagram. The USB
controller can implement a USB function endpoint, a USB host, or both for testing purposes (loop-back
diagnostics).
31.3 USB Controller Key Features
The USB function mode features are as follows:
• Four independent endpoints support control, bulk, interrupt, and isochronous data transfers
• CRC16 generation and checking
• CRC5 checking
• NRZI encoding/decoding with bit stuffing
• 12- or 1.5-Mbps data rate
Freescale Semiconductor
MPC885 PowerQUICC Family Reference Manual, Rev. 2
31-1