4 years, 6 months ago.

Why does my LPC11U37 reset?

I have a custom target using the LPC11U37. It initializes its peripherals and memory and then enters an endless loop. There are no external interrupts but I do use a timer to step my endless loop. The reset line is connected to a pushbutton switch only.

What can cause the processor to reset? I've monitored the power supply voltage and it is mostly stable at 3.3V but occasionally will have a short dip to 2.7V. However, since the part is rated to 1.8V, this does not seem like the problem.

I have compiled my project using mbed online IDE for both the LPC11U24 target and LPC11U35 target but both result in occasional reset of the target.

Any help for a weary searcher?

Thanks, KC

2 Answers

4 years, 6 months ago.

Decoupling powersupply is good. You say you only have a pushbutton on the resetpin. So I guess you rely on the internal pull up to keep the resetpin at high level. That could make the pin sensitive to static as well as powerdips. Better use an external pull up (10K) and a small cap (100n) to prevent spurious resets. Note that original mbed boards have a tendency to reset when your finger just hovers above the resetbutton..

Accepted Answer

I added a 10K pullup resistor from reset to VCC. That did not help. I then added a 0.01uF cap from reset to ground and the problem has not recurred. This seems to have fixed it in hardware. I wonder what will happen if I activate that pin as an output and just set it's value to logic 0.

As a software solution, I made the reset a general I/O pin. This works without adding the RC network on the board but you lose the reset function.

posted by Kevin Callan 24 Nov 2015
4 years, 6 months ago.

Is there any way you can reproduce the voltage dip to 2.7V?

Then maybe can you see if the voltage dip correlates with the reset on a scope. You could toggle a pin at the top of your main function to give you some indication of a reset.

If that's the case, putting some decoupling capacitors across your VCC and GND lines should help.

I have added more decoupling to the power supply (another 100uF) and it has indeed reduced the amplitude of the dip to 3.1V minimum. However, the processor continues to reset.

posted by Kevin Callan 24 Nov 2015

Hmm it should probably be able to withstand a dip of only 3.1V. I would try Wim's suggestion below.

posted by Brian Daniels 24 Nov 2015