LPC2141FBD64 Philips Semiconductors (Acquired by NXP), LPC2141FBD64 Datasheet - Page 21

• Manufacturer Part Number: LPC2141FBD64
• Manufacturer: Philips Semiconductors (Acquired by NXP)

Philips Semiconductors
9397 750 14985
Preliminary data sheet
6.19.1 Crystal oscillator
6.19.2 PLL
6.19.3 Reset and wake-up timer
6.19 System control
On-chip integrated oscillator operates with external crystal in range of 1 MHz to 25 MHz.
The oscillator output frequency is called f
referred to as CCLK for purposes of rate equations, etc. f
unless the PLL is running and connected. Refer to
information.
The PLL accepts an input clock frequency in the range of 10 MHz to 25 MHz. The input
frequency is multiplied up into the range of 10 MHz to 60 MHz with a Current Controlled
Oscillator (CCO). The multiplier can be an integer value from 1 to 32 (in practice, the
multiplier value cannot be higher than 6 on this family of microcontrollers due to the upper
frequency limit of the CPU). The CCO operates in the range of 156 MHz to 320 MHz, so
there is an additional divider in the loop to keep the CCO within its frequency range while
the PLL is providing the desired output frequency. The output divider may be set to divide
by 2, 4, 8, or 16 to produce the output clock. Since the minimum output divider value is 2,
it is insured that the PLL output has a 50 % duty cycle. The PLL is turned off and
bypassed following a chip reset and may be enabled by software. The program must
configure and activate the PLL, wait for the PLL to Lock, then connect to the PLL as a
clock source. The PLL settling time is 100 s.
Reset has two sources on the LPC2141/42/44/46/48: the RESET pin and watchdog reset.
The RESET pin is a Schmitt trigger input pin with an additional glitch filter. Assertion of
chip reset by any source starts the Wake-up Timer (see Wake-up Timer description
below), causing the internal chip reset to remain asserted until the external reset is
de-asserted, the oscillator is running, a fixed number of clocks have passed, and the
on-chip flash controller has completed its initialization.
When the internal reset is removed, the processor begins executing at address 0, which is
the reset vector. At that point, all of the processor and peripheral registers have been
initialized to predetermined values.
The Wake-up Timer ensures that the oscillator and other analog functions required for
chip operation are fully functional before the processor is allowed to execute instructions.
This is important at power on, all types of reset, and whenever any of the aforementioned
functions are turned off for any reason. Since the oscillator and other functions are turned
off during Power-down mode, any wake-up of the processor from Power-down mode
makes use of the Wake-up Timer.
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•
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Match register updates are synchronized with pulse outputs to prevent generation of
erroneous pulses. Software must ‘release’ new match values before they can become
effective.
May be used as a standard timer if the PWM mode is not enabled.
A 32-bit Timer/Counter with a programmable 32-bit Prescaler.
Rev. 01 — 3 October 2005
osc
and the ARM processor clock frequency is
LPC2141/42/44/46/48
Single-chip 16-bit/32-bit microcontrollers
Section 6.19.2 “PLL”
osc
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
and CCLK are the same value
for additional
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