need urgent help:voltmeter with 89C52

range:0-5V

i have to design a volmeter using 89C52,ADC0804 and a 1602 LCD display.i dont have enough knowledge.Could i find circuit and its assembly code or can someone help me pls?

all you need to do is calibration..
check the ADC0804 tutorial in the tutorial section. when you keep Vref/2 pin of ADC0804 open the analong voltage range is 5V.
i.e. 00 represents 0V and FF represents 5V.
for calibration just connect predefined or pre-calculated voltage at analog input and check the digital o/p then increase the voltage till you get one step increase in the digital o.p

e.g. you applied 4V and you are getting C8 as digital o/p
so increase the voltage till you get C9 at o/p
then calculate the voltage difference. lets say at C9 voltage is 4.2v
so your one step is 0.2V
just make the basic circuit of ADC0804 first.. and then move further.

thank you,i got it but my problem is LCD interfacing.One step on ADC is 0.02 V.for example i get 0000 0100 from ADC and it has to write 0.08 on LCD.i dont know how to make it

no you are not getting my point..
will explain this later..
I think you first learn LCD interfacing.. check the LCD tutorial..
visit here... http://www.8051projects.net/microcontroller-tutorials/

finaly i have made someting but this design is working on the PROTEUS but not on protoboard.any advice?