LPC2158 datasheet(22/45 Pages) NXP

22 / 45 page

LPC2157_2158_1

Product data sheet

Rev. 01 — 15 October 2008

22 of 45

NXP Semiconductors

LPC2157/2158

Single-chip 16-bit/32-bit microcontrollers

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 prescaler.

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

Tcy(PCLK) × 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.

6.18 Pulse width modulator

The PWM is based on the standard timer block and inherits all of its features, although

only the PWM function is pinned out on the LPC2157/2158. The timer is designed to count

cycles of the peripheral clock (PCLK) and optionally generate interrupts or perform other

actions when speciﬁed timer values occur, based on seven match registers. The PWM

function is also based on match register events.

The ability to separately control rising and falling edge locations allows the PWM to be

used for more applications. For instance, multi-phase motor control typically requires three

non-overlapping PWM outputs with individual control of all three pulse widths and

positions.

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