NXP Semiconductors LPC11U3x User Manual

UM10462 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2016. All rights reserved.
User manual Rev. 5.5 — 21 December 2016 29 of 523
NXP Semiconductors
UM10462
Chapter 3: LPC11U3x/2x/1x System control block
3.5.12 System PLL clock source update register
This register updates the clock source of the system PLL with the new input clock after the
SYSPLLCLKSEL register has been written to. In order for the update to take effect, first
write a zero to the SYSPLLUEN register and then write a one to SYSPLLUEN.
3.5.13 USB PLL clock source select register
This register selects the clock source for the dedicated USB PLL. The USBPLLCLKUEN
register (see Section 3.5.14
) must be toggled from LOW to HIGH for the update to take
effect.
Remark: When switching clock sources, both clocks must be running before the clock
source is updated in the USBPLLCLKUEN register. For USB operation, the clock source
must be switched from IRC to system oscillator with both the IRC and the system
oscillator running. After the switch, the IRC can be turned off.
3.5.14 USB PLL clock source update enable register
This register updates the clock source of the USB PLL with the new input clock after the
USBPLLCLKSEL register has been written to. In order for the update to take effect at the
USB PLL input, first write a zero to the USBPLLUEN register and then write a one to
USBPLLUEN.
Remark: The system oscillator must be selected in the USBPLLCLKSEL register in order
to use the USB PLL, and this register must be toggled to update the USB PLL clock with
the system oscillator.
Remark: When switching clock sources, both clocks must be running before the clock
source is updated.
Table 18. System PLL clock source update enable register (SYSPLLCLKUEN, address
0x4004 8044) bit description
Bit Symbol Value Description Reset value
0 ENA Enable system PLL clock source update 1
0 No change
1 Update clock source
31:1 - - Reserved -
Table 19. USB PLL clock source select register (USBPLLCLKSEL, address 0x4004 8048) bit
description
Bit Symbol Value Description Reset
value
1:0 SEL USB PLL clock source 0x00
0x0 IRC. The USB PLL clock source must be switched to system
oscillator for correct full-speed USB operation. The IRC is
suitable for low-speed USB operation.
0x1 System oscillator
0x2 Reserved
0x3 Reserved
31:2 - - Reserved 0x00

NXP Semiconductors LPC11U3x Specifications

General

Brand	NXP Semiconductors
Model	LPC11U3x
Category	Microcontrollers
Language	English