Why AT8051 not sensing the 3.9v in the P1.0

[sathishdn]

Hii

I am converting 12V into 3.9V Dc by using Divider network 10Kand 4.7KΩ .and this out of the divider is feeding into at8051mc port 1.0 but its and sensing the voltage.
but it wil sense the voltage when i use 470 Ω and 220Ω in the place of 10K and 4.7k.
What may be the reason Please get me a solution .

 

[bassa]

Dear sathishdn,

flowing current may be the problem.

I suggest that if you can clearly explain your problem by giving more details, I mean what you going to measure or interface, then this might be help full to understand by others and you will be able to solve your problems without any trouble and very rapidly.

Best Regards
bassa

 

[praveensss]

What is the supply voltage for the uC?
If it is 5, increase the lower resistor to get a value close to 5.Any value should then work.
Did you check the voltages with a multimeter with both combinations?

 

[CMOS]

It may be your code too. Are you making the pin high on power-up? If not, do that.
If the pin is low and you are trying to read it, what you are observing could happen.

Since P1, P2 and P3 ports of 8051 are quasi bi-directional, you need to make a pin high to use it in input mode.
I am sure you know this already but just avoiding one possibility.