UM10429
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User manual
Rev. 1 — 20 October 2010
13 of 258
NXP Semiconductors
UM10429
Chapter 3: LPC1102 System configuration
3.5.3 System PLL control register
This register connects and enables the system PLL and configures the PLL multiplier and
divider values. The PLL accepts an input frequency from 10 MHz to 25 MHz from various
clock sources. The input frequency is multiplied up to a high frequency, then divided down
to provide the actual clock used by the CPU, peripherals, and memories. The PLL can
produce a clock up to the maximum allowed for the CPU.
3.5.4 System PLL status register
This register is a Read-only register and supplies the PLL lock status (see
3.5.5 System oscillator control register
This register configures the frequency range for the system oscillator.
Table 8.
System PLL control register (SYSPLLCTRL, address 0x4004 8008) bit description
Bit
Symbol
Value
Description
Reset
value
4:0
MSEL
Feedback divider value. The division value M is the
programmed MSEL value + 1.
00000: Division ratio M = 1
to
11111: Division ration M = 32
0x000
6:5
PSEL
Post divider ratio P. The division ratio is 2
×
P.
0x00
0x0
P = 1
0x1
P = 2
0x2
P = 4
0x3
P = 8
31:7
-
-
Reserved. Do not write ones to reserved bits.
0x0
Table 9.
System PLL status register (SYSPLLSTAT, address 0x4004 800C) bit description
Bit
Symbol
Value
Description
Reset
value
0
LOCK
PLL lock status
0x0
0
PLL not locked
1
PLL locked
31:1
-
-
Reserved
0x00
Table 10.
System oscillator control register (SYSOSCCTRL, address 0x4004 8020) bit
description
Bit
Symbol
Value
Description
Reset
value
0
BYPASS
Bypass system oscillator
0x0
0
Oscillator is not bypassed.
1
Bypass enabled. PLL input (sys_osc_clk) is fed
directly from the XTALIN pin.