srikanth,

1)
Ensure that your power supply doesn't bounce below the power fail detect threshold.

2)
How do you select the RAM or is CE always enabled?

3)
Reviewing the Data sheet @:

http://quetzal.uis.edu.co/ciee-html...lus121.pdf

I don't see any parameter that would invalidate use at 12MHz std 8051.

3)
Does you comment that ex0/1 are disabled also mean all other sources of interrupt are disabled (i.e. EA=0)?

4)
Try writing your messages to the RAM using a Read after Write approach to validate that the RAM is being addressed and written correctly. If the "read after write" validates, then you know the problem is in the LCD update portion.

Let me know.

regards,
p