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USB Registers
1796
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Universal Serial Bus (USB) Controller
27.5.79 USBCC Register (Offset = 0xFC8) [reset = 0x0]
USB Clock Configuration (USBCC)
The USBCC register specifies the clock configuration for the USB controller.
NOTE:
When the USB module uses the integrated USB PHY, the MOSC must be the clock source,
either with or without using the PLL, and the system clock must be at least 30 MHz. In
addition, only integer divisors should be used to achieve the 60 MHz USB clock source.
Fractional divisors may increase jitter and compromise USB function.
USBCC is shown in
and described in
Return to
Figure 27-92. USBCC Register
31
30
29
28
27
26
25
24
RESERVED
R-0x0
23
22
21
20
19
18
17
16
RESERVED
R-0x0
15
14
13
12
11
10
9
8
RESERVED
CLKEN
CSD
R-0x0
R/W-0x0
R/W-0x0
7
6
5
4
3
2
1
0
RESERVED
CLKDIV
R-0x0
R/W-0x0
Table 27-99. USBCC Register Field Descriptions
Bit
Field
Type
Reset
Description
31-10
RESERVED
R
0x0
9
CLKEN
R/W
0x0
USB Clock Enable.
This bit enables the 60 MHz clock used for the USB PHY.
This bit must always be set when using the USB, regardless of
whether the PHY is internal or external.
0x0 = USB clock is disabled.
0x1 = USB clock is enabled.
8
CSD
R/W
0x0
Clock Source/Direction.
This bit specifies the source of the 60 MHz USB PHY clock when
using ULPI.
0x0 = Internal Source. USB0CLK is an output to the external ULPI
PHY and is configured using the following equation:
PLL_VCO/( 1)
0x1 = External Source. USB0CLK is an input from the ULPI external
PHY.
7-4
RESERVED
R
0x0
3-0
CLKDIV
R/W
0x0
PLL Clock Divisor.
This field specifies the divisor used to reduce the PLL VCO output to
the 60 MHz clock source required for the serialization and
deserialization module of the USB controller.
The divisor value is the CLKDIV value plus 1.