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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
589 of 808
NXP Semiconductors
UM10360
Chapter 32: LPC17xx Flash memory interface and programming
3.1.1 Criterion for Valid User Code
The reserved Cortex-M3 exception vector location 7 (offset 0x 001C in the vector table)
should contain the 2’s complement of the check-sum of table entries 0 through 6. This
causes the checksum of the first 8 table entries to be 0. The boot loader code checksums
the first 8 locations in sector 0 of the flash. If the result is 0, then execution control is
transferred to the user code.
If the signature is not valid, the auto-baud routine synchronizes with the host via serial port
0. The host should send a “?” (0x3F) as a synchronization character and wait for a
response. The host side serial port settings should be 8 data bits, 1 stop bit and no parity.
The auto-baud routine measures the bit time of the received synchronization character in
terms of its own frequency and programs the baud rate generator of the serial port. It also
sends an ASCII string ("Synchronized<CR><LF>") to the host. In response to this the host
should send the same string ("Synchronized<CR><LF>"). The auto-baud routine looks at
the received characters to verify synchronization. If synchronization is verified then
"OK<CR><LF>" string is sent to the host. The host should respond by sending the crystal
frequency (in kHz) at which the part is running. For example, if the part is running at 10
MHz, the response from the host should be "10000<CR><LF>". "OK<CR><LF>" string is
sent to the host after receiving the crystal frequency. If synchronization is not verified then
Fig 134. Map of lower memory