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UM10375
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© NXP B.V. 2011. All rights reserved.
User manual
Rev. 3 — 14 June 2011
321 of 368
NXP Semiconductors
UM10375
Chapter 21: LPC13xx Flash memory programming firmware
21.7 Criterion for Valid User Code
The reserved ARM Cortex-M3 exception vector location 7 (offset 0x0000 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 bootloader
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 the serial
port (UART) or boots from the USB port (PIO0_3 is sampled HIGH).
If the UART is selected, 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 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. 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 the auto-baud routine waits again
for a synchronization character. For auto-baud to work correctly in case of user invoked
ISP, the CCLK frequency should be greater than or equal to 10 MHz. In UART ISP mode,
the LPC13xx is clocked by the IRC and the crystal frequency is ignored.
For more details on Reset, PLL and startup/boot code interaction see
Once the crystal frequency is received the part is initialized and the ISP command handler
is invoked. For safety reasons an "Unlock" command is required before executing the
commands resulting in flash erase/write operations and the "Go" command. The rest of
the commands can be executed without the unlock command. The Unlock command is
required to be executed once per ISP session. The Unlock command is explained in
Section 21.13 “ISP commands” on page 328
21.8 ISP/IAP communication protocol
All ISP commands should be sent as single ASCII strings. Strings should be terminated
with Carriage Return (CR) and/or Line Feed (LF) control characters. Extra <CR> and
<LF> characters are ignored. All ISP responses are sent as <CR><LF> terminated ASCII
strings. Data is sent and received in UU-encoded format.
21.8.1 ISP command format
"Command Parameter_0 Parameter_1 ... Parameter_n<CR><LF>" "Data" (Data only for
Write commands).
21.8.2 ISP response format
"Return_Code<CR><LF>Response_0<CR><LF>Response_1<CR><LF> ...
Response_n<CR><LF>" "Data" (Data only for Read commands).