UM10462
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User manual
Rev. 5.5 — 21 December 2016
35 of 523
NXP Semiconductors
UM10462
Chapter 3: LPC11U3x/2x/1x System control block
3.5.24 USB clock divider register
This register allows the USB clock usb_clk to be divided to 48 MHz. The usb_clk can be
shut down by setting the DIV bits to 0x0.
3.5.25 CLKOUT clock source select register
This register selects the signal visible on the CLKOUT pin. Any oscillator or the main clock
can be selected.
Bit 0 of the CLKOUTUEN register (see
) must be toggled from 0 to 1 for the
update to take effect.
3.5.26 CLKOUT clock source update enable register
This register updates the clock source of the CLKOUT pin with the new clock after the
CLKOUTSEL register has been written to. In order for the update to take effect at the input
of the CLKOUT pin, first write a zero to bit 0 of this register, then write a one.
Table 29.
USB clock source update enable register (USBCLKUEN, address 0x4004 80C4) bit
description
Bit
Symbol
Value
Description
Reset value
0
ENA
Enable USB clock source update
0x0
0
No change
1
Update clock source
31:1
-
-
Reserved
0x00
Table 30.
USB clock divider register (USBCLKDIV, address 0x4004 80C8) bit description
Bit
Symbol
Description
Reset value
7:0
DIV
USB clock divider values
0: Disable USB clock.
1: Divide by 1.
to
255: Divide by 255.
0x01
31:8
-
Reserved
0x00
Table 31.
CLKOUT clock source select register (CLKOUTSEL, address 0x4004 80E0) bit
description
Bit
Symbol
Value
Description
Reset
value
1:0
SEL
CLKOUT clock source
0
0x0
IRC oscillator
0x1
Crystal oscillator (SYSOSC)
0x2
LF oscillator (watchdog oscillator)
0x3
Main clock
31:2
-
-
Reserved
0