USB 2.0
Subsystem
(USB0)
AUXCLK
USB_
REFCLKIN
1
0
CFGCHIP2[USB0PHYCLKMUX]
Introduction
1608
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Universal Serial Bus 2.0 (USB) Controller
34.1.4 Industry Standard(s) Compliance Statement
This device conforms to USB 2.0 Specification.
34.2 Architecture
34.2.1 Clock Control
shows the clock connections for the USB2.0 module. Note that there is no built-in oscillator.
The USB2.0 subsystem requires a reference clock for its internal PLL. This reference clock can be
sourced from either the USB_REFCLKIN pin or from the AUXCLK of the system PLL. The reference clock
input to the USB2.0 subsystem is selected by programming the USB0PHYCLKMUX bit in the chip
configuration 2 register (CFGCHIP2) of the System Configuration Module. The USB_REFCLKIN source
should be selected when it is not possible (such as when specific audio rates are required) to operate the
device at one of the allowed input frequencies to the USB2.0 subsystem. The USB2.0 subsystem
peripheral bus clock is sourced from SYSCLK2.
determines the source origination as well as
the source input frequency to the USB 2.0 PHY. Once the clock source origination (internal/external) and
its frequency is determined, the firmware should program the PHY PLL with the correct input frequency via
CFGCHIP2.USB0REF_FREQ (see
).
NOTE:
Prior to accessing any of the device configuration registers, including CFGCHIP2, in order to
avoid inadvertent access, two Access Key Registers (KICK0R and KICK1R) should be
written with key values. For more information on the device configuration registers, see your
device-specific data manual.
Figure 34-2. USB Clocking Diagram