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we have 89c51 microcontroller. how to insert program in it ? and can we remove the microcontroller from PCB
Read the documentation the manufacturer has provided, it is highly unlikely they did not give instructions on how to program the processor, and if you made it here you certainly can read the manufacturers information.
As for removing it from the PCB, why do you need to worry about it? I am sure you know exactly what you are asking, however I can't guess what you have. You might considered adding those 'details' you would want to know like MANUFACTURE a COMPLETE PART NUMBER, SURFACE MOUNT/ THROUGH HOLE, is the PCB something 'you designed' or is it an Evaluation Board? If it was designed by 'you' then 'you' should get the documentation on the design, if it is an evaluation board get that boards documentation. Programming the processor is part of the design, you should already HAVE this documentation, if not then something is quite amiss.
You choose the wrong subject, as THAT is not C251 compatible micro-controller.
Stephen