Thanks friends,

I have seen all the sites referred by you both.

OK now there is much more clarity and the thing is well under control.Have managed to get it to life and basic functions like horizontal lines and vertical lines of any specified width etc are through.

I tried to draw a box and have run into a serious problem. Let me explain it briefly.

I am drawing a Box that has two pixel wide margins on the periphery of the display area.

I start with the TopHorizontal, then do the RightVertical , then the BottomHorizontal and then the LeftVertical.

The problem is with the LeftVertical alone.

Here is the code

LVerLine: clr	Select
          mov	r3,  #0b8h      ;start with first page
VerLup1:  mov	a,  #40h	;problem here...
     	  call	Write_Instr     ;1st Column CS1 
     	  mov	a,  r3          ;page address
     	  call	Write_Instr     
     	  mov	a,  #0ffh
     	  call	Write_Data
     	  mov	a,  #0ffh
     	  call	Write_Data
     	  inc	r3              ;next page now
     	  cjne	r3, #0c0h, VerLup1
     	  ret

I always end up getting a kind of staircase - the first page is Ok, but the next page has the line offset by 2 columns and so on. But if I change the starting column addres to anything other than #40h things are fine . Like if I make it #41h I get a straight line at that column, upto the bottom.

OK I am not using Busy bit checking, but each Data/Instr write has a built in 200microsecond delay. And the other three lines are drawing perfect.

Any tips / guesses ? I am going nuts..


Thanks

Raghu