
UM10800
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2016. All rights reserved.
User manual
Rev. 1.2 — 5 October 2016
44 of 487
NXP Semiconductors
UM10800
Chapter 5: LPC82x System configuration (SYSCON)
5.6.16 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.
5.6.17 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.
5.6.18 CLKOUT clock divider register
This register determines the divider value for the signal on the CLKOUT pin.
5.6.19 USART fractional generator divider value register
All USART peripherals share a common clock U_PCLK, which can be adjusted by a
fractional divider:
Table 37.
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
Watchdog oscillator
0x3
Main clock
31:2
-
-
Reserved
0
Table 38.
CLKOUT clock source update enable register (CLKOUTUEN, address 0x4004
80E4) bit description
Bit
Symbol
Value
Description
Reset value
0
ENA
Enable CLKOUT clock source update
0
0
No change
1
Update clock source
31:1
-
-
Reserved
-
Table 39.
CLKOUT clock divider registers (CLKOUTDIV, address 0x4004 80E8) bit
description
Bit
Symbol
Description
Reset
value
7:0
DIV
CLKOUT clock divider values
0: Disable CLKOUT clock divider.
1: Divide by 1.
to
255: Divide by 255.
0
31:8
-
Reserved
-