I use 89C51ED2 (44 pin PLCC) in my circuit and I am facing a peculiar problem. The reset circuit of micro-controller consists of 8.2K and 10uF capacitor. When powered on the reset pin (PIN 10) remains in HIGH state, even though it is pulled down to ground by 8.2K resistor. I checked that RESET pin is not shorted to VCC. This problem persists only in a few PCBs and rest of the PCBs works fine. I have used identical components in all PCBs. But when I remove the micro controller, PIN 10 of IC base comes to LOW state. What can be the reason for this problem? Thanks in advance.
always in HIGH state
scope or VOM?, if VOM try a scope
I have measured the voltage using oscilloscope and it is around 4.9VDC.
hardware problem, you may have better luck here http://www.8052.com/forum/