NXP Semiconductors LPC24XX UM10237 - Manual (Page 44)

UM10237_4 © NXP B.V. 2009. All rights reserved.
User manual Rev. 04 — 26 August 2009 44 of 792
NXP Semiconductors
UM10237
Chapter 4: LPC24XX Clocking and power control
Since chip operation always begins using the Internal RC Oscillator, and the main
oscillator may never be used in some applications, it will only be started by software
request. This is accomplished by setting the OSCEN bit in the SCS register, as described
in
Table 3–38 . The main oscillator provides a status flag (the OSCSTAT bit in the SCS
Fig 13. Oscillator modes and models: a) slave mode of operation, b) oscillation mode of operation, c) external
crystal model used for C
X1
/
X2
evaluation
LPC24xx LPC24xx
Clock
C
i
C
X1
C
X2
C
L
C
P
L
R
S
< = >
a) b) c)
Xtal
XTAL1 XTAL2 XTAL1 XTAL2
C
g
Table 39. Recommended values for C
X1/X2
in oscillation mode (crystal and external
components parameters) low frequency mode (OSCRANGE = 0, see Table 3–38 )
Fundamental
oscillation frequency
F
OSC
Crystal load
capacitance C
L
Maximum crystal
series resistance R
S
External load
capacitors C
X1
,
CX2
1 MHz - 5 MHz 10 pF < 300
Ω
18 pF, 18 pF
20 pF < 300
Ω
39 pF, 39 pF
30 pF < 300
Ω
57 pF, 57 pF
5 MHz - 10 MHz 10 pF < 300
Ω
18 pF, 18 pF
20 pF < 200
Ω
39 pF, 39 pF
30 pF < 100
Ω
57 pF, 57 pF
10 MHz - 15 MHz 10 pF < 160
Ω
18 pF, 18 pF
20 pF < 60
Ω
39 pF, 39 pF
15 MHz - 20 MHz 10 pF < 80
Ω
18 pF, 18 pF
Table 40. Recommended values for C
X1/X2
in oscillation mode (crystal and external
components parameters) high frequency mode (OSCRANGE = 1, see Table 3–38 )
Fundamental
oscillation frequency
F
OSC
Crystal load
capacitance C
L
Maximum crystal
series resistance R
S
External load
capacitors C
X1
,
CX2
15 MHz - 20 MHz 10 pF < 180
Ω
18 pF, 18 pF
20 pF < 100
Ω
39 pF, 39 pF
20 MHz - 25 MHz 10 pF < 160
Ω
18 pF, 18 pF
20 pF < 80
Ω
39 pF, 39 pF