LPC2131 datasheet(26/41 Pages) PHILIPS

26 / 41 page

9397 750 14868

Preliminary data sheet

Rev. 02 — 15 April 2005

26 of 41

Philips Semiconductors

LPC2131/2132/2134/2136/2138

Single-chip 16/32-bit microcontrollers

When the internal reset is removed, the processor begins executing at address 0, which is

the reset vector. At that point, all of the processor and peripheral registers have been

initialized to predetermined values.

The wake-up timer ensures that the oscillator and other analog functions required for chip

operation are fully functional before the processor is allowed to execute instructions. This

is important at power on, all types of reset, and whenever any of the aforementioned

functions are turned off for any reason. Since the oscillator and other functions are turned

off during Power-down mode, any wake-up of the processor from Power-down mode

makes use of the wake-up timer.

The wake-up timer monitors the crystal oscillator as the means of checking whether it is

safe to begin code execution. When power is applied to the chip, or some event caused

the chip to exit Power-down mode, some time is required for the oscillator to produce a

signal of sufﬁcient amplitude to drive the clock logic. The amount of time depends on

many factors, including the rate of VDD ramp (in the case of power on), the type of crystal

and its electrical characteristics (if a quartz crystal is used), as well as any other external

circuitry (e.g. capacitors), and the characteristics of the oscillator itself under the existing

ambient conditions.

6.21.4 Brown-out detector

The LPC2131/2132/2134/2136/2138 include 2-stage monitoring of the voltage on the VDD

pins. If this voltage falls below 2.9 V, the BOD asserts an interrupt signal to the Vectored

Interrupt Controller. This signal can be enabled for interrupt; if not, software can monitor

the signal by reading dedicated register.

The second stage of low-voltage detection asserts reset to inactivate the

LPC2131/2132/2134/2136/2138 when the voltage on the VDD pins falls below 2.6 V. This

reset prevents alteration of the Flash as operation of the various elements of the chip

would otherwise become unreliable due to low voltage. The BOD circuit maintains this

reset down below 1 V, at which point the POR circuitry maintains the overall reset.

Both the 2.9 V and 2.6 V thresholds include some hysteresis. In normal operation, this

hysteresis allows the 2.9 V detection to reliably interrupt, or a regularly-executed event

loop to sense the condition.

6.21.5 Code security

This feature of the LPC2131/2132/2134/2136/2138 allow an application to control whether

it can be debugged or protected from observation.

If after reset on-chip boot-loader detects a valid checksum in Flash and reads

0x87654321 from address 0x1FC in Flash, debugging will be disabled and thus the code

in Flash will be protected from observation. Once debugging is disabled, it can be enabled

only by performing a full chip erase using the ISP.

6.21.6 External interrupt inputs

The LPC2131/2132/2134/2136/2138 include up to nine edge or level sensitive External

Interrupt Inputs as selectable pin functions. When the pins are combined, external events

can be processed as four independent interrupt signals. The External Interrupt Inputs can

optionally be used to wake up the processor from Power-down mode.

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