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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
44 of 808
NXP Semiconductors
UM10360
Chapter 4: LPC17xx Clocking and power control
6.4.1 PLL1 modes
The combinations of PLLE1 and PLLC1 are shown in
6.5 PLL1 Interrupt: PLOCK1
The PLOCK1 bit in the PLL1STAT register reflects the lock status of PLL1. When PLL1 is
enabled, or parameters are changed, the PLL requires some time to establish lock under
the new conditions. PLOCK1 can be monitored to determine when the PLL may be
connected for use.
PLOCK1 is connected to the interrupt controller. This allows for software to turn on the
PLL and continue with other functions without having to wait for the PLL to achieve lock.
When the interrupt occurs, the PLL may be connected, and the interrupt disabled.
PLOCK1 appears as interrupt 48 in
. Note that PLOCK1 remains asserted
whenever PLL1 is locked, so if the interrupt is used, the interrupt service routine must
disable the PLOCK1 interrupt prior to exiting.
Table 31.
PLL1 Status register (PLL1STAT - address 0x400F C0A8) bit description
Bit
Symbol
Description
Reset
value
4:0
MSEL1
Read-back for the PLL1 Multiplier value. This is the value currently
used by PLL1.
0
6:5
PSEL1
Read-back for the PLL1 Divider value. This is the value currently
used by PLL1.
0
7
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
8
PLLE1_STAT Read-back for the PLL1 Enable bit. When one, PLL1 is currently
activated. When zero, PLL1 is turned off. This bit is automatically
cleared when Power-down mode is activated.
0
9
PLLC1_STAT Read-back for the PLL1 Connect bit. When PLLC and PLLE are
both one, PLL1 is connected as the clock source for the
microcontroller. When either PLLC or PLLE is zero, PLL1 is
bypassed and the oscillator clock is used directly by the
microcontroller. This bit is automatically cleared when Power-down
mode is activated.
0
10
PLOCK1
Reflects the PLL1 Lock status. When zero, PLL1 is not locked.
When one, PLL1 is locked onto the requested frequency.
0
15:11 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
Table 32.
PLL1 control bit combinations
PLLC1 PLLE1 PLL1 Function
0
0
PLL1 is turned off and disconnected.
0
1
PLL1 is active, but not yet connected. PLL1 can be connected after PLOCK1 is
asserted.
1
0
Same as 00 combination. This prevents the possibility of PLL1 being
connected without also being enabled.
1
1
PLL1 is active and has been connected. The clock for the USB subsystem is
sourced from PLL1.