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USB 2.0
Subsystem
(USB0)
AUXCLK
USB_
REFCLKIN
1
0
CFGCHIP2[USB0PHYCLKMUX]
Peripheral Clocking
Table 6-3. Example PLL Frequencies
OSCIN
Multiplier
Frequency
PLL Multiplier
Frequency
Div1
Div2
Div3
Div4
20
30
600 MHz
Not Supported
300
200
150
24
25
600 MHz
Not Supported
300
200
150
25
24
600 MHz
Not Supported
300
200
150
30
20
600 MHz
Not Supported
300
200
150
20
25
500 MHz
Not Supported
250
167
125
24
20
480 MHz
Not Supported
240
160
120
25
18
450 MHz
Not Supported
225
150
112.5
30
14
420 MHz
Not Supported
210
140
105
25
16
400 MHz
Not Supported
200
133
100
6.3
Peripheral Clocking
6.3.1 USB Clocking
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 PLL0_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.
Figure 6-2. USB Clocking Diagram
Table 6-4. USB Clock Multiplexing Options
CFGCHIP2.
USB2.0
USB0PHYCLKMUX
Clock
bit
Source
Additional Conditions
0
USB_REFCLKIN
USB_REFCLKIN must be 12, 24, 48, 19.2, 38.4, 13, 26, 20, or 40 MHz. The
PLL inside the USB2.0 PHY can be configured to accept any of these input
clock frequencies.
1
PLL0_AUXCLK
PLL0_AUXCLK must be 12, 24, 48, 19.2, 38.4, 13, 26, 20, or 40 MHz. The
PLL inside the USB2.0 PHY can be configured to accept any of these input
clock frequencies.
63
SPRUGX5A
–
May 2011
Device Clocking
Copyright
©
2011, Texas Instruments Incorporated
Содержание AM1802
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