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UM10237_2
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 02 — 19 December 2008
48 of 792
NXP Semiconductors
UM10237
Chapter 4: LPC24XX Clocking and power control
[1]
Reset Value reflects the data stored in used bits only. It does not include reserved bits content.
3.2.4 PLL Control register (PLLCON - 0xE01F C080)
The PLLCON register contains the bits that enable and connect the PLL. Enabling the
PLL allows it to attempt to lock to the current settings of the multiplier and divider values.
Connecting the PLL causes the processor and all chip functions to run from the PLL
output clock. Changes to the PLLCON register do not take effect until a correct PLL feed
sequence has been given (see
Section 4–3.2.9 “PLL Feed register (PLLFEED -
The PLL must be set up, enabled, and Lock established before it may be used as a clock
source. When switching from the oscillator clock to the PLL output or vice versa, internal
circuitry synchronizes the operation in order to ensure that glitches are not generated.
Hardware does not insure that the PLL is locked before it is connected or automatically
Table 43.
PLL registers
Name
Description
Access Reset
value
Address
PLLCON
PLL Control Register. Holding register for
updating PLL control bits. Values written to this
register do not take effect until a valid PLL feed
sequence has taken place.
R/W
0
0xE01F C080
PLLCFG
PLL Configuration Register. Holding register for
updating PLL configuration values. Values
written to this register do not take effect until a
valid PLL feed sequence has taken place.
R/W
0
0xE01F C084
PLLSTAT
PLL Status Register. Read-back register for
PLL control and configuration information. If
PLLCON or PLLCFG have been written to, but
a PLL feed sequence has not yet occurred, they
will not reflect the current PLL state. Reading
this register provides the actual values
controlling the PLL, as well as the PLL status.
RO
0
0xE01F C088
PLLFEED
PLL Feed Register. This register enables
loading of the PLL control and configuration
information from the PLLCON and PLLCFG
registers into the shadow registers that actually
affect PLL operation.
WO
NA
0xE01F C08C
Table 44.
PLL Control register (PLLCON - address 0xE01F C080) bit description
Bit
Symbol
Description
Reset
value
0
PLLE
PLL Enable. When one, and after a valid PLL feed, this bit will
activate the PLL and allow it to lock to the requested frequency. See
PLLSTAT register,
.
0
1
PLLC
PLL Connect. Having both PLLC and PLLE set to one followed by a
valid PLL feed sequence, the PLL becomes the clock source for the
CPU, as well as the USB subsystem and. Otherwise, the clock
selected by the Clock Source Selection Multiplexer is used directly
by the LPC2400. See PLLSTAT register,
.
0
7:2
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA