Hi I am having start up problems with lpc23xx devices. i.e sometimes the CPU does not start my code when power is connected I activated brown out by changing PCON register and the situation got better when I reduce the pull up resistor or the capacitor I have on the reset pin, the situation gets better
Finally I removed the capacitor and the was only a 39k pull up resistor on reset pin and the problem was solved. The core was starting normal operation each time I connected power
My question is that will this cause a problem if I don't use a capacitor on reset pin? What other solution do you suggest to solve this problem?
Thanks I looked at my supply voltage by oscilloscope and there was 500mV AC on my 3.3V Although I had 10 x100nF capacitors on the chip I added an electrolytic capacitor and now my circuit starts working even when I have 100nF capacitor on reset pin
Just there is one more problem. I have a switch that connects reset pin to GND. When I apply a low to the reset pin, the chip stops and doesn't restart when I remove the low level on the reset pin Maybe the chip is entering ISP mode. but I have a 10K pull up resistor on P2.10. what else should I do? This is interesting that when jtag connector is connected to the board, the reset switch works fine and the CPU restarts normally after reset
R-C based reset circuits are a notoriously poor design choice, they will fail if the supply rise time is too slow, or if the reset glitches or the supply browns out.
The use of a power-on-reset chip (Microchip has a couple, MCP120?), is strongly recommended to get a predictable and consistent reset pulse.
R-C based reset circuits are a notoriously poor design choice, they will fail if the supply rise time is too slow, or if the reset glitches or the supply browns out. and always fail on power down.
Erik
power down problems are, almost, invariably reported as power up problems.