help me in DAC using 89c4051

ya, your are correct, mcu will provide the reference voltage. while designing we need to set the reference voltage. But the problem here is how to start the comparison? do i need to write software coding for that or it keeps on comparing? As you said we need to enable the comparator i.e set bit CEN of ACSR. but 89c4051 does not have ACSR. what to do? please help me bit in coding... help me in coding how to start comparing? using interrupt or enabling comparator? or any other metods? if you have code please post it

ya, your are correct, mcu will provide the reference voltage. while designing we need to set the reference voltage. But the problem here is how to start the comparison? do i need to write software coding for that or it keeps on comparing? As you said we need to enable the comparator i.e set bit CEN of ACSR. but 89c4051 does not have ACSR. what to do? please help me bit in coding... help me in coding how to start comparing? using interrupt or enabling comparator? or any other metods? if you have code please post it

For the AT89C4051 microcontroller the output of analog comparator is defined as:
"P3.6 is hard-wired as an input to the output of the on-chip comparator and is not accessible as a general-purpose I/O pin."
www.atmel.com/.../doc1001.pdf

The "next" model of AT89S4051 has the ACSR SFR (and PWM also)
www.atmel.com/.../doc3390.pdf

Thank you sir, you helped me a lot.

Sir, mcu 89v51rd2 is not communicating serially. rs232 cable is working.
mcu was communicating 4 days before, but now it is not communicating.. I have lost 2 mcu. what would be the problem?

Is this the same project with AT89C4051 with DAC/ADC or another one?
Is there a problem in serial communication with another device ?
Is there a problem with ISP ?
Please describe the issue (mcu, board, connections), a "not working" is not enough.

The problem got resolved, now its working. I don't know exactly where the problem was. sometimes communication happens and sometimes it won't communicate...

Thank you

mcu 89v51rd2 is not communicating serially. rs232 cable is working.
mcu was communicating 4 days before, but now it is not communicating.. I have lost 2 mcu. what would be the problem?
check that your MAX232(equivalent) is connected correctly.
do not remember how, but remember it was the transciever connection

Erik

The problem got resolved, now its working. I don't know exactly where the problem was.

Then the problem has not been resolved. It's just gone away for now. But if you don't know what the problem was, then it cannot possibly have been resolved.