I am programming a graphic lcd using PIC18f87J90

Though I am writing the data to the lcd for both the left and right half of the display,

the data on the left half disappears

Sometimes the code works fine giving exact data on both the left half and right half.

But often the left half part doesn't work.

I am not sure if there is problem with my code or there is issue with the graphic lcd

If anyone has an idea please let me know
Thanks

 

Usually problems that only occur some of the time like this are due to intermittent connections. If sometimes only the left half doesn't work you can rule out everything that is common between them except for the line that determines if the left or right side is being addressed. This may be the highest address line, or a chip select (CS) line.

What may be happening is this line opens so the display never sees the chip select for the side that doesn't get updated.

More information here from you may help.