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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
31 of 368
NXP Semiconductors
UM10375
Chapter 3: LPC13xx System configuration
3.5.30 CLKOUT clock source select register
This register configures the clkout_clk signal to be output on the CLKOUT pin. All three
oscillators and the main clock can be selected for the clkout_clk clock.
The CLKOUTCLKUEN register (see
) 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.
3.5.31 CLKOUT clock source update enable register
This register updates the clock source of the CLKOUT pin with the new clock after the
CLKOUTCLKSEL 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 the CLKCLKUEN register and then write a
one to CLKCLKUEN.
Remark:
When switching clock sources, both clocks must be running before the clock
source is updated.
3.5.32 CLKOUT clock divider register
This register determines the divider value for the clkout_clk signal on the CLKOUT pin.
Table 37.
CLKOUT clock source select register (CLKOUTCLKSEL, address 0x4004 80E0) bit
description
Bit
Symbol
Value
Description
Reset
value
1:0
SEL
CLKOUT clock source
0x00
0x0
IRC oscillator
0x1
System oscillator
0x2
Watchdog oscillator
0x3
Main clock
31:2
-
-
Reserved
0x00
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
0x0
0
No change
1
Update clock source
31:1
-
-
Reserved
0x00