Nxp Semiconductors UM10237 Manuale Utente

UM10237_2

© NXP B.V. 2008. All rights reserved.

 

On the assertion of any of reset sources (POR, BOD reset, External reset and Watchdog 
reset), the following two sequences start simultaneously:

1. After IRC-start-up time (maximum of 60 

μs on power-up), IRC provides stable clock 

output, the reset signal is latched and synchronized on the IRC clock. The 2-bit IRC 
wakeup timer starts counting when the synchronized reset is de-asserted. The boot 
code in the ROM starts when the 2-bit IRC wakeup timer times out. The boot code 
performs the boot tasks and may jump to the flash. If the flash is not ready to access, 
the MAM will insert wait cycles until the flash is ready.

2. After IRC-start-up time (maximum of 60 

μs on power-up), IRC provides stable clock 

output, the reset signal is synchronized on the IRC clock. The flash wakeup-timer 
(9-bit) starts counting when the synchronized reset is de-asserted. The flash 
wakeup-timer generates the 100 

μs flash start-up time. Once it times out, the flash 

initialization sequence is started, which takes about 250 cycles. When it’s done, the 
MAM will be granted access to the flash.

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. 

 shows an example of the relationship between the RESET, the IRC, and the 

processor status when the LPC2400 starts up after reset. For the start-up sequence of the 
main oscillator if enabled by the user code, see 

.

C

Q

S

APB read of
PDBIT
in PCON

power

down

C

Q

S

F

OSC

to other
blocks

WAKEUP TIMER

watchdog

reset

external

reset

START

COUNT 2 

n

internal RC

oscillator

Reset to the
on-chip circuitry

Reset to
PCON.PD

write “1”

from APB

reset

EINT0 wakeup
EINT1 wakeup

EINT2 wakeup

POR

BOD

EINT3 wakeup

RTC wakeup

BOD wakeup

Ethernet MAC wakeup

USB need_clk  wakeup

CAN  wakeup

GPIO0 port wakeup
GPIO2 port wakeup