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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
27 of 571
NXP Semiconductors
UM10316
Chapter 3: LPC29xx Clock Generation Unit (CGU)
3.1 Controlling the XO50M oscillator (external oscillator)
The XO50M oscillator can be disabled using the ENABLE field in the oscillator control
register. Even when enabled, this can be bypassed using the BYPASS field in the same
register. In this case the input of the OSC1M crystal is fed directly to the output.
The XO50M oscillator has an HF pin which selects the operating mode. For operation at
higher frequencies (15-25 MHz), the XO50M oscillator HF must be enabled. For
frequencies below that the pin must be disabled. Setting of the pin is controlled by the HF
in the oscillator control register.
3.2 Controlling the PL160M PLL
The structure of the PLL clock path is shown in
Fig 11. Structure of the clock generation scheme
PLL160M
FDIV0..6
XO50M
OSC1M
Clock
outputs
clkout /
clkout120 /
clkout240
Output
Control