LPC2101_02_03_3

© NXP B.V. 2008. All rights reserved.

Product data sheet

Rev. 03 — 7 October 2008

17 of 32

NXP Semiconductors

LPC2101/02/03

Single-chip 16-bit/32-bit microcontrollers

6.16 Real-time clock

The Real-Time Clock (RTC) is designed to provide a set of counters to measure time

when normal or idle operating mode is selected. The RTC has been designed to use little

power, making it suitable for battery powered systems where the CPU is not running

continuously (Idle mode).

6.16.1 Features

of Year.

external crystal/oscillator input at XTAL1. The programmable reference clock divider

allows fine adjustment of the RTC.

6.17 System control

6.17.1 Crystal oscillator

On-chip integrated oscillator operates with external crystal in range of 1 MHz to 25 MHz.

unless the PLL is running and connected. Refer to Section 6.17.2 “PLL” for additional

information.

6.17.2 PLL

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 70 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, and then connect to the PLL as a

clock source. The PLL settling time is 100

µs.