UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
44 of 1269
NXP Semiconductors
UM10503
Chapter 5: LPC43xx Boot ROM
5.3.6 Boot process timing
The following parameters describe the timing of the boot process:
[1]
For flashless parts LPC1850/30/20/10.
[2]
For parts with on-chip flash; booting from flash.
[3]
For parts with on-chip flash; booting from an external source.
Fig 17. USB boot process
Setup clock
USB_CLK=60MHz
Setup VBUS pin P2_5
Boot
source?
USB1
USB0
Setup clock
USB_CLK=480MHz
Enable HS PHY
DFU
enumerate
receive image
see main boot flow
Table 22.
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