5V vs. 3.3V in LPC2106

Started by kanok53 April 3, 2009
I have a question regarding the 5V tolerant IO pin of lpc2106. I need to measure a pulse width connected to the capture0 pin of lpc2106. and notice that the signal voltage is 0-5v range. I'm measuring the pulse duration by trapping the rising edge and falling edge capture interrupt. now is that okay to measure the pulse of 0-5V range by LPC2106? I'm facing peculiar problem sometime to measure this. it doesn't give correct answer but if i short the cap0.0 pin to the rx0 pin momentarily then it give correct result all the time.
now how can you explain this peculiar event?
by the way, I'm using usart0 for serial communication. and my prototype board is from OLIMEX.

An Engineer's Guide to the LPC2100 Series