© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 01 — 15 August 2005
18
Philips Semiconductors
UM10139
Volume 1
Chapter 3: System Control Block
[1]
Reset value reflects the data stored in used bits only. It does not include reserved bits content.
3.4 Crystal oscillator
While an input signal of 50-50 duty cycle within a frequency range from 1 MHz to 50 MHz
can be used by the LPC2141/2/4/6/8 if supplied to its input XTAL1 pin, this
microcontroller’s onboard oscillator circuit supports external crystals in the range of 1 MHz
to 30 MHz only. If the on-chip PLL system or the boot-loader is used, the input clock
frequency is limited to an exclusive range of 10 MHz to 25 MHz.
The oscillator output frequency is called F
OSC
and the ARM processor clock frequency is
referred to as CCLK for purposes of rate equations, etc. elsewhere in this document. F
OSC
and CCLK are the same value unless the PLL is running and connected. Refer to the
Section 3.8 “Phase Locked Loop (PLL)” on page 27
for details and frequency limitations.
The onboard oscillator in the LPC2141/2/4/6/8 can operate in one of two modes: slave
mode and oscillation mode.
In slave mode the input clock signal should be coupled by means of a capacitor of 100 pF
(C
C
in
, drawing a), with an amplitude of at least 200 mVrms. The X2 pin in this
configuration can be left not connected. If slave mode is selected, the F
OSC
signal of 50-50
duty cycle can range from 1 MHz to 50 MHz.
External components and models used in oscillation mode are shown in
,
drawings b and c, and in
. Since the feedback resistance is integrated on chip, only
a crystal and the capacitances C
X1
and C
X2
need to be connected externally in case of
fundamental mode oscillation (the fundamental frequency is represented by L, C
L
and
R
S
). Capacitance C
P
in
, drawing c, represents the parallel package capacitance
and should not be larger than 7 pF. Parameters F
C
, C
L
, R
S
and C
P
are supplied by the
crystal manufacturer.
Choosing an oscillation mode as an on-board oscillator mode of operation limits F
OSC
clock selection to 1 MHz to 30 MHz.
CSPR
Code Security Protection Register
RO
0
0xE01F C184
Syscon Miscellaneous Registers
SCS
System Controls and Status
R/W
0
0xE01F C1A0
Table 6:
Summary of system control registers
Name
Description
Access
Reset
value
[1]
Address