UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 49 of 792
NXP Semiconductors UM10237
Chapter 4: LPC24XX Clocking and power control

disconnect the PLL if lock is lost during operation. In the event of loss of PLL lock, it is

likely that the oscillator clock has become unstable and disconnecting the PLL will not

remedy the situation.

3.2.5 PLL Configuration register (PLLCFG - 0xE01F C084)

The PLLCFG register contains the PLL multiplier and divider values. Changes to the

PLLCFG register do not take effect until a correct PLL feed sequence has been given (see

Section 4–3.2.9 “PLL Feed register (PLLFEED - 0xE01F C08C)). Calculations for the

PLL frequency, and multiplier and divider values are found in the Section 4��3.2.11 “PLL

frequency calculation.

Table 45. PLL Configuration register (PLLCFG - address 0xE01F C084) bit description
Bit Symbol Description Reset
value
14:0 MSEL PLL Multiplier value. Supplies the value "M" in the PLL frequency
calculations. The value stored here is M - 1. Supported values for M
are 6 through 512 and those listed in Table4–46 .
Note: Not all values of M are needed, and therefore some are not
supported by hardware. For details on selecting values for MSEL see
Section 4–3.2.11 “PLL frequency calculation.
0
15 - Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined. NA
23:16 NSEL PLL Pre-Divider value. Supplies the value "N" in the PLL frequency
calculations. PLL Pre-Divider value. Supplies the value "N" in the PLL
frequency calculations. Supported values for N are 1 through 32.
Note: For details on selecting the right value for NSEL see Section
4–3.2.11 “PLL frequency calculation.
0
31:24 - Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined. NA
Table 46. Multiplier values for a 32 kHz oscillator
Multiplier (M) Pre-divide (N) FCCO
4272 1 279.9698
4395 1 288.0307
4578 1 300.0238
4725 1 309.6576
4807 1 315.0316
5127 1 336.0031
5188 1 340.0008
5400 1 353.8944
5493 1 359.9892
5859 1 383.9754
6042 1 395.9685
6075 1 398.1312
6104 1 400.0317
6409 1 420.0202
6592 1 432.0133
6750 1 442.3680