ARM7 datasheet(19/38 Pages) PHILIPS

19 / 38 page

9397 750 14985

Preliminary data sheet

Rev. 01 — 3 October 2005

19 of 38

Philips Semiconductors

LPC2141/42/44/46/48

Single-chip 16-bit/32-bit microcontrollers

– Reset timer on match with optional interrupt generation.

• Four external outputs per timer/counter corresponding to match registers, with the

following capabilities:

– Set LOW on match.

– Set HIGH on match.

– Toggle on match.

– Do nothing on match.

6.16 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.

6.16.1 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 pre-scaler.

• Selectable time period from (TPCLK × 256 × 4) to (TPCLK × 232 × 4) in multiples of

TPCLK × 4.

6.17 Real-time clock

The 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).

6.17.1 Features

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

• Ultra-low power design to support battery powered systems.

• Provides Seconds, Minutes, Hours, Day of Month, Month, Year, Day of Week, and Day

of Year.

• Can use either the RTC dedicated 32 kHz oscillator input or clock derived from the

external crystal/oscillator input at XTAL1. Programmable reference clock divider

allows ﬁne adjustment of the RTC.

• Dedicated power supply pin can be connected to a battery or the main 3.3 V.

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