LPC2468 datasheet(39/72 Pages) NXP

39 / 72 page

LPC2468_4

Product data sheet

Rev. 04 — 17 October 2008

39 of 72

NXP Semiconductors

LPC2468

Fast communication chip

• Pulse period and width can be any number of timer counts. This allows complete

ﬂexibility in the trade-off between resolution and repetition rate. All PWM outputs will

occur at the same repetition rate.

• Double edge controlled PWM outputs can be programmed to be either positive going

or negative going pulses.

• 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.

7.23 Watchdog timer (WDT)

The purpose of the watchdog is to reset the microcontroller within a reasonable amount of

time if it enters an erroneous state. When enabled, the watchdog will generate a system

reset if the user program fails to ‘feed’ (or reload) the watchdog within a predetermined

amount of time.

7.23.1 Features

• Internally resets chip if not periodically reloaded.

• Debug mode.

• Enabled by software but requires a hardware reset or a watchdog reset/interrupt to be

disabled.

• Incorrect/Incomplete feed sequence causes reset/interrupt if enabled.

• Flag to indicate watchdog reset.

• Programmable 32-bit timer with internal prescaler.

• Selectable time period from (Tcy(WDCLK) × 256 × 4) to (Tcy(WDCLK) × 232 × 4) in

multiples of Tcy(WDCLK) × 4.

• The Watchdog Clock (WDCLK) source can be selected from the RTC clock, the

Internal RC oscillator (IRC), or the APB peripheral clock. This gives a wide range of

potential timing choices of Watchdog operation under different power reduction

conditions. It also provides the ability to run the WDT from an entirely internal source

that is not dependent on an external crystal and its associated components and

wiring, for increased reliability.

7.24 RTC and battery RAM

The RTC is a set of counters for measuring time when system power is on, and optionally

when it is off. It uses little power in Power-down mode. On the LPC2468, the RTC can be

clocked by a separate 32.768 kHz oscillator or by a programmable prescale divider based

on the APB clock. Also, the RTC is powered by its own power supply pin, VBAT, which can

be connected to a battery or to the same 3.3 V supply used by the rest of the device.

The VBAT pin supplies power only to the RTC and the Battery RAM. These two functions

require a minimum of power to operate, which can be supplied by an external battery.

When the CPU and the rest of chip functions are stopped and power removed, the RTC

can supply an alarm output that can be used by external hardware to restore chip power

and resume operation.

LPC2468 Datasheet(PDF) 39 Page - NXP Semiconductors

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