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Peripheral Clocking
120
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Device Clocking
Table 6-3. Example PLL Frequencies
OSCIN
Frequency
PLL Multiplier
Multiplier
Frequency
Div1
Div2
Div3
Div4
20
30
600 MHz
600
300
200
150
24
25
600 MHz
600
300
200
150
25
24
600 MHz
600
300
200
150
30
20
600 MHz
600
300
200
150
20
25
500 MHz
500
250
167
125
24
20
480 MHz
480
240
160
120
25
18
450 MHz
450
225
150
112.5
30
14
420 MHz
420
210
140
105
25
16
400 MHz
400
200
133
100
6.3
Peripheral Clocking
6.3.1 USB Clocking
shows the clock connections for the USB2.0 module. 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.
The USB1.1 subsystem requires both a 48 MHz (CLK48) and a 12 MHz (CLK12) clock input. The 12 MHz
clock is derived from the 48 MHz clock. The 48 MHz clock required by the USB1.1 subsystem can be
sourced from either the USB_REFCLKIN or from the 48 MHz clock provided by the USB2.0 PHY. The
CLK48 source is selected by programming the USB1PHYCLKMUX bit in CFGCHIP2 of the System
Configuration Module. The USB1.1 subsystem peripheral bus clock is sourced from PLL0_SYSCLK4. See
NOTE:
If the USB1.1 subsystem is used and the 48 MHz clock input is sourced from the USB2.0
PHY, then the USB2.0 must be configured to always generate the 48 MHz clock. The
USB0PHY_PLLON bit in CFGCHIP2 controls the USB2.0 PHY, allowing or preventing it from
stopping the 48 MHz clock during USB SUSPEND. When the USB0PHY_PLLON bit is set to
1, the USB2.0 PHY is prevented from stopping the 48 MHz clock during USB SUSPEND;
when the USB0PHY_PLLON bit is cleared to 0, the USB2.0 PHY is allowed to stop the
48 MHz clock during USB SUSPEND.