LPC23xx ISP baudrate confusion

[PPi]

Greetings,

I wish someone could shred some light in here, as I have a problem that goes beyond my understanding. I have a few LPC23xx based designs that I program via ISP using Flash Magic. However I seem to get reliable results only with baud rates 9600 or 19200 but not higher. So far it seems that only about 20% to 30% of boards tested succeeds with 57600 while others just don't seem to give any response to the programming software.

The NXP LPC23xx user manual says:

When ISP mode is entered after a power on reset, the IRC and PLL are used to generate the CCLK of 14.748 MHz. The baud rates that can easily be obtained in this case are: 9600 Bd, 19200 Bd, 38400 Bd, 57600 Bd, 115200 Bd, and 230400 Bd.

Can it be that the IRC of the NXP is just so inaccurate that it may lead to communications fail? This problem clearly isn't about poor layout design or such as I have tried this with other boards as well. Using different computers may have affect but this would be poor solution. Have I missed something in here? What are your experiences?

[Andy Ayre]

Based on my experience I would be very surprised to get anything above 38400 baud when auto bauding when using something like 14MHz.

Andy