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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
200 of 1441
NXP Semiconductors
UM10503
Chapter 13: LPC43xx/LPC43Sxx Clock Generation Unit (CGU)
13.7.4.3.5
Mode 1d: Normal operating mode with post-divider and with pre-divider
In normal operating mode 1d none of the dividers are bypassed. The operating
frequencies are:
Fout = Fcco /(2 x P) = M x Fin /(N x P)
(275 MHz
Fcco
550 MHz, 4 kHz
Fin/N
150
MHz)
The divider ratios are programmable:
•
Pre-divider N (N, 1 to 256)
•
Feedback-divider M (M, 1 to 2
15
)
•
Post-divider P (P, 1 to 32)
13.7.4.3.6
Mode 3: Power down mode (pd)
In this mode (pd = '1'), the oscillator will be stopped, the lock output will be made low, and
the internal current reference will be turned off. During pd it is also possible to load new
divider ratios at the input buses (msel, psel, nsel). Power-down mode is ended by making
pd low, causing the PLL to start up. The lock signal will be made high once the PLL has
regained lock on the input clock.
13.7.4.4 Settings for USB0
shows the divider settings used for configuring an output frequency F
out
of
480 MHz for USB0.
13.7.4.5 Usage notes
In order to set up the PLL0, follow these steps:
1. Power down the PLL0 by setting bit 0 in the PLL0 control register (PLL0USB_CTRL or
PLL0AUDIO_CTRL) to 1. This step is only needed if the PLL0 is currently enabled.
2. Configure the PLL0 m, n, and p divider values in the PLL0_M and PLL0_NP registers.
3. Power up the PLL0 by setting bit 0 in the PLL0 control (PLL0USB_CTRL or
PLL0AUDIO_CTRL) register to 0.
4. Wait for the PLL0 to lock by monitoring the LOCK bit in the PLL0_STAT register.
5. Enable the PLL0 clock output in the PLL0_CTRL register.
Remark:
You can change the PLL0 settings while the PLL0 is running when you need to
configure the PLL0 for high output frequencies (see
13.7.5 Fractional divider for PLL0AUDIO
The PLL0 for audio applications (PLL0AUDIO) includes an additional fractional divider.
The SEL_EXT bit in the PLL0AUDIO control register determines whether the fractional
divider is used (SEL_EXT=0) or bypassed (SEL_EXT=1). In the latter case, PLL0AUDIO
operates exactly as PLL0USB and the MDEC value is used directly to control the
feedback divider.
When the fractional divider is active, the sigma-delta modulator block generates divider
values M and M+1 in the correct proportion so that an average division ratio of M+K/L is
realized where 0<=K<=L and M, K, and L are integer values. M Is determined by the
integer part of the PLLFRACT_CTRL register (PLLFRACT[21:15]) and K is determined by