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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
105 of 1441
NXP Semiconductors
UM10503
Chapter 7: LPC43Sxx Boot ROM for secure parts
[1]
For flashless parts LPC43S50/S30/S20.
[2]
For parts with on-chip flash; booting from flash.
[3]
For parts with on-chip flash; booting from an external source.
Table 75.
Typical boot process timing parameters
Parameter
Description
Value
t_a
Check boot selection pins
< 1.25
s
t_b
Initialize device
250
; 180
s
; 200
t_c
Copy image to embedded SRAM
If part is executing from external
flash with no copy
< 0.3
s
If the image is encrypted or must
be copied
< 1
s to 10000
s
depending on the size of the image and the
speed of the boot memory
Fig 29. Boot process timing
GND
VDDREG
IRC12
RESET
supply
ramp up
IRC12
starts
IRC12
stable
22 μs
0.5μs; IRC stability count
valid
threshold
boot time
user code
processor status
t
a
μs
t
b
μs
t
c
μs
check boot
selection
pins
copy image to
embedded
SRAM
initialise
device