Datasheet

LPC2388_0 © NXP B.V. 2007. All rights reserved.
Preliminary data sheet Rev. 00.01 — 23 October 2007 30 of 57
NXP Semiconductors
LPC2388
Fast communication chip
7.23 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.
7.23.1 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 (T
cy(WDCLK)
× 256 × 4) to (T
cy(WDCLK)
× 2
32
× 4) in
multiples of T
cy(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 LPC2388, 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.
7.24.1 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.
• Dedicated 32 kHz oscillator or programmable prescaler from APB clock.
• Dedicated power supply pin can be connected to a battery or to the main 3.3 V.