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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
35 of 808
NXP Semiconductors
UM10360
Chapter 4: LPC17xx Clocking and power control
5.6 PLL0 Interrupt: PLOCK0
The PLOCK0 bit in the PLL0STAT register reflects the lock status of PLL0. When PLL0 is
enabled, or parameters are changed, PLL0 requires some time to establish lock under the
new conditions. PLOCK0 can be monitored to determine when PLL0 may be connected
for use. The value of PLOCK0 may not be stable when the PLL reference frequency
(F
REF
, the frequency of REFCLK, which is equal to the PLL input frequency divided by the
pre-divider value) is less than 100 kHz or greater than 20 MHz. In these cases, the PLL
may be assumed to be stable after a start-up time has passed. This time is 500
μ
s when
FREF is greater than 400 kHz and 200 / FREF seconds when FREF is less than 400 kHz
PLOCK0 is connected to the interrupt controller. This allows for software to turn on PLL0
and continue with other functions without having to wait for PLL0 to achieve lock. When
the interrupt occurs, PLL0 may be connected, and the interrupt disabled. PLOCK0
appears as interrupt 32 in
. Note that PLOCK0 remains asserted whenever
PLL0 is locked, so if the interrupt is used, the interrupt service routine must disable the
PLOCK0 interrupt prior to exiting.
5.7 PLL0 Modes
The combinations of PLLE0 and PLLC0 are shown in
Table 22.
PLL Status register (PLL0STAT - address 0x400F C088) bit description
Bit
Symbol
Description
Reset
value
14:0
MSEL0
Read-back for the PLL0 Multiplier value. This is the value currently
used by PLL0, and is one less than the actual multiplier.
0
15
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA
23:16 NSEL0
Read-back for the PLL0 Pre-Divider value. This is the value
currently used by PLL0, and is one less than the actual divider.
0
24
PLLE0_STAT Read-back for the PLL0 Enable bit. This bit reflects the state of the
PLEC0 bit in PLL0CON (see
) after a valid PLL0 feed.
When one, PLL0 is currently enabled. When zero, PLL0 is turned
off. This bit is automatically cleared when Power-down mode is
entered.
0
25
PLLC0_STAT Read-back for the PLL0 Connect bit. This bit reflects the state of
the PLLC0 bit in PLL0CON (see
) after a valid PLL0
feed.
When PLLC0 and PLLE0 are both one, PLL0 is connected as the
clock source for the CPU. When either PLLC0 or PLLE0 is zero,
PLL0 is bypassed. This bit is automatically cleared when
Power-down mode is entered.
0
26
PLOCK0
Reflects the PLL0 Lock status. When zero, PLL0 is not locked.
When one, PLL0 is locked onto the requested frequency. See text
for details.
0
31:27 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
NA