hi
i m using 89c51 , the output voltage of port1 is approx 5 volt, but i need 12 voltage as my requirement, i used simple NPN transistor, but the output is approx same with base voltage, actually i want to use it for digital clock, where 6 LEDs in one series, so 42 LEDs are in one segment, so how can i get 12 voltage as output for 7 segment, as i told the base voltage is 4.5-5 voltage
This has nothing at all to do with Keil!
It would be far more appropriate at http://www.8052.com/forum
In fact, there is already plenty there to help you; eg, www.8052.com/.../162273
Note the specific issue of using NPN transistors with "classic" 8051 ports...