Nikhil,

Welcome. This time your question is written better. However you said:


Please elaborate this point.

What I have got from your post is that you want to display a line on the CRT of your oscilloscope. Am I right?

If that is the case then you need 2 different DC voltage sources in order to drive a CRO in X-Y mode. Now the question that how it can be done with 8051, has many possible answers/solutions.

1) Use 8051 to generate PWM, then adequate filtering of the PWM will give you a DC voltage. This might be good only if you need to draw simple lines.
2) Better use 2 DACs (Digital to Analog Converter) and you can display anything on CRO, though difficult to display complex graphics/objects. Don't expect that you can display high quality JPEG images on CRO :-).

Displaying a single (horizontal or vertical) line require just constant DC voltages on both inputs as you have figured out already.

Regarding Intel 8275, this chip is (or may be was) a programmable CRT controller. I couldn't find datasheet to have a look at it. Instead take some time to read this application note from Intel.
AP-223 8051 Based CRT Terminal Controller

May be we can suggest much better solution if you describe in more detail what I have asked in the beginning