Nxp Semiconductors UM10237 用户手册

UM10237_2

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Sequence based on round-robin.

The LPC2400 includes 2-stage monitoring of the voltage on the V

DD(3V3)

 pins. If this 

voltage falls below 2.95 V, the Brown-Out Detector (BOD) asserts an interrupt signal to 
the Vectored Interrupt Controller. This signal can be enabled for interrupt in the Interrupt 
Enable Register in the VIC (see 

) in order to cause a CPU interrupt; if not, software can monitor the signal 

by reading the Raw Interrupt Status Register (see 

).

The second stage of low-voltage detection asserts Reset to inactivate the LPC2400 when 
the voltage on the V

DD(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.

But when Brown-Out Detection is enabled to bring the LPC2400 out of Power-Down mode 
(which is itself not a guaranteed operation -- see 

), the supply voltage may recover from a transient before 

the Wakeup Timer has completed its delay. In this case, the net result of the transient 
BOD is that the part wakes up and continues operation after the instructions that set 
Power-Down Mode, without any interrupt occurring and with the BOD bit in the RSID 
being 0. Since all other wakeup conditions have latching flags (see 

 and 

), a wakeup 

of this type, without any apparent cause, can be assumed to be a Brown-Out that has 
gone away.

Applications in development typically need the debugging and tracing facilities in the 
LPC2400. Later in the life cycle of an application, it may be more important to protect the 
application code from observation by hostile or competitive eyes. The following feature of 
the LPC2400 allows an application to control whether it can be debugged or protected 
from observation.

Details on the way Code Read Protection works can be found in 

Remark: CRP is not available for flashless LPC2400 parts.

13:12

EP1

CPU

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18:16

EP2

Ethernet

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