I have a LPC11E67 and in ISP mode it responds to the "?" character on UART0-RX with a very low baud rate (10 bps). The content of the answer back itself is ok (Synchronized). What could be the reason?

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I have a LPC11E67 and in ISP mode it responds to the "?" character on UART0-RX with a very low baud rate (10 bps). The content of the answer back itself is ok (Synchronized). What could be the reason?

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Contributor I

The signal on the scope is the answer measured on UART0-TX (so not reset as in the picture itself!!)154268_154268.pngtek00002.png

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NXP TechSupport
NXP TechSupport

Hi Hans,

First of, I was wondering if you can illustrate the completely procedure of replicating the kind of issue, then can you update the application program through the ISP successful or not?

I'm looking forward to your reply.
Have a great day,
Ping

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Contributor I

Hi Jeremy,

The programming procedure is as follows:

1. Hold the ISP_EN input low by pressing a push button.

2. Power the LPC11E67, which then goes into ISP mode.

3. The RXD0 and TXD0 of the LPC11E67 are connected to a MCP2221 USB-UART transceiver, so the LPC can be programmed with FlashMagic via USB.

4. The LPC gives corrected response, but with a very low baudrate, which is different each time.

Next I tried the following procedure, which works:

1. Power the board

2. Hold reset and ISP input low

3. Make reset high

4. Make ISP high

5. The device is now in ISP mode, and responds with the correct baudrate.

So it looks like the LPC is determining the baudrate wrongly during power-up in ISP mode. When extending the power-up reset time (larger capacitor on reset input) to >200ms, the baudrate is ok. So the problem is:

1. Power-up in normal operation: short power-up reset (small or no cap on reset input): everything ok, so baudrate ok

2. Power-up in ISP mode by holding ISP input low: reset time >200ms is needed to have correct baudrate on UART0

Hope you can help!

Regards,

Hans

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NXP TechSupport
NXP TechSupport

Hi Hans,

Thanks for your reply.

First of all, I will follow the procedure to replicate the phenomenon, then report the kind of the phenomenon to the AE team for checking after the verification.
Have a great day,

Ping

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