LPC2387 datasheet(27/52 Pages) NXP

27 / 52 page

LPC2387_3

Product data sheet

Rev. 03 — 29 October 2008

27 of 52

NXP Semiconductors

LPC2387

Single-chip 16-bit/32-bit microcontroller

• 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.

7.22 Watchdog timer

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.

7.22.1 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.

7.23 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 LPC2387, 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.

7.23.1 Features

• Measures the passage of time to maintain a calendar and clock.

• Ultra low power design to support battery powered systems.

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