LPC1766_0.02
© NXP B.V. 2008. All rights reserved.
Objective data sheet
Rev. 00.02 — 12 August 2008
35 of 70
NXP Semiconductors
LPC1766
Fast communication chip
7.30 System control
7.30.1 Reset
Reset has four sources on the LPC1766: the RESET pin, the Watchdog reset, power-on
reset (POR), and the BrownOut Detection (BOD) circuit. The RESET pin is a Schmitt
trigger input pin. Assertion of chip Reset by any source, once the operating voltage attains
a usable level, starts the Wake-up timer (see description in Section 7.29.5), causing reset
to remain asserted until the external Reset is de-asserted, the oscillator is running, a fixed
number of clocks have passed, and the flash controller has completed its initialization.
When the internal Reset is removed, the processor begins executing at address 0, which
is initially the Reset vector mapped from the Boot Block. At that point, all of the processor
and peripheral registers have been initialized to predetermined values.
7.30.2 Brownout detection
The LPC1766 includes 2-stage monitoring of the voltage on the VREG(3V3) pins. If this
voltage falls below 2.95 V, the BOD asserts an interrupt signal to the Vectored Interrupt
Controller. This signal can be enabled for interrupt in the Interrupt Enable Register in the
NVIC in order to cause a CPU interrupt; if not, software can monitor the signal by reading
a dedicated status register.
The second stage of low-voltage detection asserts Reset to inactivate the LPC1766 when
the voltage on the VREG(3V3) pins falls below 2.65 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 power-on reset circuitry maintains the overall Reset.
Both the 2.95 V and 2.65 V thresholds include some hysteresis. In normal operation, this
hysteresis allows the 2.95 V detection to reliably interrupt, or a regularly executed event
loop to sense the condition.
7.30.3 Code security (Code Read Protection - CRP)
This feature of the LPC1766 allows user to enable different levels of security in the system
so that access to the on-chip flash and use of the JTAG and ISP can be restricted. When
needed, CRP is invoked by programming a specific pattern into a dedicated flash location.
IAP commands are not affected by the CRP.
There are three levels of the Code Read Protection.
CRP1 disables access to chip via the JTAG and allows partial flash update (excluding
flash sector 0) using a limited set of the ISP commands. This mode is useful when CRP is
required and flash field updates are needed but all sectors can not be erased.
CRP2 disables access to chip via the JTAG and only allows full flash erase and update
using a reduced set of the ISP commands.
Running an application with level CRP3 selected fully disables any access to chip via the
JTAG pins and the ISP. This mode effectively disables ISP override using P2[10] pin, too.
It is up to the user’s application to provide (if needed) flash update mechanism using IAP
calls or call reinvoke ISP command to enable flash update via UART0.
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