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Philips Semiconductors
Preliminary User Manual
LPC2119/2129/2292/2294
ARM-based Microcontroller
The two writes must be in the correct sequence, and must be consecutive VPB bus cycles. The latter requirement implies that
interrupts must be disabled for the duration of the PLL feed operation. If either of the feed values is incorrect, or one of the
previously mentioned conditions is not met, any changes to the PLLCON or PLLCFG register will not become effective.
PLL and Power Down Mode
Power Down mode automatically turns off and disconnects the PLL. Wakeup from Power Down mode does not automatically
restore the PLL settings, this must be done in software. Typically, a routine to activate the PLL, wait for lock, and then connect
the PLL can be called at the beginning of any interrupt service routine that might be called due to the wakeup. It is important not
to attempt to restart the PLL by simply feeding it when execution resumes after a wakeup from Power Down mode. This would
enable and connect the PLL at the same time, before PLL lock is established.
PLL Frequency Calculation
The PLL equations use the following parameters:
F
OSC
the frequency from the crystal oscillator
F
CCO
the frequency of the PLL current controlled oscillator
cclk
the PLL output frequency (also the processor clock frequency)
M
PLL Multiplier value from the MSEL bits in the PLLCFG register
P
PLL Divider value from the PSEL bits in the PLLCFG register
The PLL output frequency (when the PLL is both active and connected) is given by:
F
cco
cclk = M * F
osc
or cclk =
———
2 * P
The CCO frequency can be computed as:
F
cco
= cclk * 2 * P or F
cco
= F
osc
* M * 2 * P
The PLL inputs and settings must meet the following:
• F
osc
is in the range of 10 MHz to 25 MHz.
• cclk is in the range of 10 MHz to F
max
(the maximum allowed frequency for the LPC2119/2129/2292/2294).
• F
cco
is in the range of 156 MHz to 320 MHz.
Table 26: PLL Feed Register (PLLFEED - 0xE01FC08C)
PLLFEED
Function
Description
Reset
Value
7:0
PLLFEED
The PLL feed sequence must be written to this register in order for PLL
configuration and control register changes to take effect.
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