UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
69 of 1441
NXP Semiconductors
UM10503
Chapter 6: LPC43xx/LPC43Sxx flash programming/ISP and IAP
6.4.1 Sampling of pin P2_7
Assuming that power supply pins are on their nominal levels when the rising edge on
RESET pin is generated, it may take up to 3 ms before P2_7 is sampled and the decision
on whether to continue with user code or ISP handler is made.
If a valid user program is found, then the execution control is transferred to it. If a valid
user program is not found, the boot process defaults to the ISP mode using USART0 and
the auto-baud routine is invoked.
Pin P2_7 is used as a hardware request signal for ISP and requires special attention. It is
recommended to provide external hardware (a pull-up resistor or other device) to put the
pin in a defined state. Otherwise unintended entry into ISP mode may occur.
6.4.2 Boot process for flashless parts
for the boot process flowchart for flashless parts. If P2_7 is HIGH, the boot
code samples the OTP and the boot pins to determine the boot source. If P2_7 is LOW,
the boot code configures USART0 for ISP communication.