UM10237_2 © NXP B.V. 2008. All rights reserved.
User manual Rev. 02 — 19 December 2008 678 o f 792
NXP Semiconductors UM10237
Chapter 30: LPC24XX Flash memory programming firmware
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 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.
For more details on Reset, PLL and startup/boot code interaction see Section 4–3.2.2
“PLL and startup/boot code interaction”.
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 30–9 “ISP commands” on page 683.
5.2 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.

5.2.1 ISP command format

"Command Parameter_0 Parameter_1 ... Parameter_n<CR><LF>" "Data" (Data only for
Write commands).

5.2.2 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).

5.2.3 ISP data format

The data stream is in UU-encode format. The UU-encode algorithm converts 3 bytes of
binary data in to 4 bytes of printable ASCII character set. It is more efficient than Hex
format which converts 1 byte of binary data in to 2 bytes of ASCII hex. The sender should
send the check-sum after transmitting 20 UU-encoded lines. The length of any
UU-encoded line should not exceed 61 characters(bytes) i.e. it can hold 45 data bytes.
The receiver should compare it with the check-sum of the received bytes. If the
check-sum matches then the receiver should respond with "OK<CR><LF>" to continue
further transmission. If the check-sum does not match the receiver should respond with
"RESEND<CR><LF>". In response the sender should retransmit the bytes.