UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
125 of 1269
NXP Semiconductors
UM10503
Chapter 11: LPC43xx Clock Generation Unit (CGU)
11.7 Functional description
11.7.1 32 kHz oscillator
The 32 kHz oscillator output is controlled by the CREG block (see
). The RTC
and the Alarm timer are connected directly to the 32 kHz oscillator.
11.7.2 IRC
The IRC is a trimmed 12 MHz internal oscillator. Although the IRC is part of the CGU, the
CGU has no control over this clock source. The IRC is put into power down depending on
the power saving mode.
11.7.3 Crystal oscillator
The crystal oscillator is controlled by the XTAL_OSC_CTRL register in the CGU (see
).
11.7.4 PLL0 (PLL0USB and PLL0AUDIO)
The PLL blocks of the PLL0USB and PLL0AUDIO are identical. The PLL0AUDIO
supports an additional fractional divider to obtain more PLL frequencies with higher
accuracy for audio applications.
28:24
CLK_SEL
Clock-source selection.
0x01
R/W
0x00
32 kHz oscillator
0x01
IRC (default)
0x02
ENET_RX_CLK
0x03
ENET_TX_CLK
0x04
GP_CLKIN
0x05
Reserved
0x06
Crystal oscillator
0x07
PLL0USB
0x08
PLL0AUDIO
0x09
PLL1
0x0C
IDIVA
0x0D
IDIVB
0x0E
IDIVC
0x0F
IDIVD
0x10
IDIVE
31:29
-
Reserved
-
-
Table 91.
BASE_CGU_OUT0_CLK to BASE_CGU_OUT1_CLK control register
(BASE_CGU_OUT0_CLK to BASE_CGU_OUT1_CLK , addresses 0x4005 00C4 to
0x4005 00C8) bit description
…continued
Bit
Symbol
Value
Description
Reset
value
Access