Philips LPC2119 User Manual page 61

Philips Semiconductors
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.
Table 26: PLL Feed Register (PLLFEED - 0xE01FC08C)
PLLFEED Function
7:0 PLLFEED
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 the frequency from the crystal oscillator
OSC
F the frequency of the PLL current controlled oscillator
CCO
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:
cclk = M * F or cclk =
osc
The CCO frequency can be computed as:
F = cclk * 2 * P or
cco
The PLL inputs and settings must meet the following:
• F is in the range of 10 MHz to 25 MHz.
osc
• cclk is in the range of 10 MHz to F
• F is in the range of 156 MHz to 320 MHz.
cco
System Control Block
The PLL feed sequence must be written to this register in order for PLL
configuration and control register changes to take effect.
F
cco
———
2 * P
F = F * M * 2 * P
cco osc
(the maximum allowed frequency for the LPC2119/2129/2292/2294).
max
LPC2119/2129/2292/2294
Description
61
Preliminary User Manual
Reset
Value
undefined
January 08, 2004