NXP Semiconductors LPC24XX UM10237 - Manual (Page 699)

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User manual Rev. 04 — 26 August 2009 699 of 792
NXP Semiconductors
UM10237
Chapter 31: LPC24XX On-chip bootloader for flashless parts
4.2.1 ISP command format
"Command Parameter_0 Parameter_1 ... Parameter_n" "Data" (Data only for
Write commands).
4.2.2 ISP response format
"Return_CodeResponse_0Response_1 ...
Response_n" "Data" (Data only for Read commands).
4.2.3 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" to continue
further transmission. If the check-sum does not match the receiver should respond with
"RESEND". In response the sender should retransmit the bytes.
A description of UU-encode is available at the wotsit webpage.
4.2.4 ISP flow control
A software XON/XOFF flow control scheme is used to prevent data loss due to buffer
overrun. When the data arrives rapidly, the ASCII control character DC3 (stop) is sent to
stop the flow of data. Data flow is resumed by sending the ASCII control character DC1
(start). The host should also support the same flow control scheme.
4.2.5 ISP command abort
Commands can be aborted by sending the ASCII control character "ESC". This feature is
not documented as a command under "ISP Commands" section. Once the escape code is
received the ISP command handler waits for a new command.
4.2.6 Interrupts during ISP
The boot block interrupt vectors located in the boot ROM sector are active after any reset.
For details on mapping the interrupt vectors see
Table 2–21 .
4.2.7 Interrupts during IAP
IAP calls can be interrupted and an adequate interrupt service routine can be executed if
interrupts are enabled. For details on how the address for an interrupt service routine will
be determined, see
Table 2–19 . The IAP code does not use or disable interrupts.
4.2.8 RAM used by ISP command handler
ISP commands use on-chip RAM from 0x4000 0120 to 0x4000 01FF. The user could use
this area, but the contents may be lost upon reset. The ROM boot loader also uses the top
32 bytes of on-chip RAM. The stack is located at RAM top - 32. The maximum stack
usage is 256 bytes and grows downwards.