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Chapter 20
Universal Serial Bus Interface – On-The-Go Module
20.1
Introduction
This chapter describes the universal serial bus (USB) interface, which implements many industry
standards. However, it is beyond the scope of this document to document the intricacies of these standards.
Instead, reader should refer to the governing specifications. Readers of this chapter are assumed to be
fluent in the operation and requirements of a USB network.
Visit the USB Implementers Forum web page at
•
Universal Serial Bus Specification, Revision 2.0
•
On-The-Go Supplement to the USB 2.0 Specification, Revision 1.0a
Visit the Intel USB specifications web page at
•
Enhanced Host Controller Interface Specification for Universal Serial Bus, Revision 1.0
20.1.1
Overview
The USB On-The-Go (OTG) module is a USB 2.0-compliant serial interface engine for implementing a
USB interface. The registers and data structures are based on the Enhanced Host Controller Interface
Specification for Universal Serial Bus (EHCI) from Intel Corporation. The USB OTG module can act as
a host, a device, or an On-The-Go negotiable host/device on the USB bus.
The USB 2.0 OTG module interfaces to the processor's ColdFire core. The USB controller is
programmable to support host, or device operations under firmware control. Full-speed (FS) and
low-speed (LS) applications are supported by the integrated on-chip transceiver. The processor's on-chip
PLL provides all necessary clocks to the USB controller, including a system interface clock and a 60 MHz
clock. For special applications, pin access (via USBCLKIN) is provided for an external 60 MHz reference
clock. See
Section 9.3.4, "Miscellaneous Control Register
The USB controller provides control and status signals to interface with external USB OTG and USB host
power devices. Use these control and status signals on the chip interface and the I
with external USB On-The-Go and USB host power devices.
USB-host modules must supply 500 mA with a 5 V supply on its downstream port (referred to as VBUS);
however, the USB OTG standard provides a minimum 8 mA VBUS supply requirement. Optionally, the
OTG module may supply up to 500 mA to the USB-connected devices. If the connected device attempts
to draw more than the allocated amount of current, the USB host must disable the port and remove power.
USB VBUS is not provided on-chip. This processor provides pins for control and status to an external IC
capable of managing the VBUS downstream supply.
Freescale Semiconductor
http://www.usb.org/developers/docs
http://www.intel.com/technology/usb/spec.htm
(MISCCR)," for more information.
MCF52277 Reference Manual, Rev. 1
for:
for:
2
C bus to communicate
20-1
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