Hi Prahlad,
Can you show the schematic of the LCD connected to the CPU (both for RD2 and 668).

You can try the following methods to clear your doubts.

1. Start the serial port of your CPU. Establish the connection between your product and the Computer.

2. Write a small code to just read the variable which is stored in the Program memory. something like this:
(the following code is for Keil)

   ....
   code unsigned char TestByte=0x55;
   ....

void main (void)
{
unsigned char i;
i=TestByte;

}

3. compile this code. Start the debugger in Keil, and watch the program flow in Assembler Window. You should see that "i" will be containing 0x55 when the last instruction is executed. If it works here then you can proceed to the following code:

....
code unsigned char TestByte=0x55;
...
void main(void)
{
unsigned char i;
...
SerialPortInitialize ();     // initialize your serial port here
i=TestByte;        // Read byte into IRAM (already tested above)
TransmitByte (i); // Transmit the byte from IRAM          
TransmitByte (TestByte);  // Transmit the byte from Program mem.
for (;;);
}

You should 2 recieve the byte 0x55 (ASCII Char 'U'). This will guide you to the exact problem you are facing.

If there is a hardware interfacing problem with the LCD (due to any reason), then you will recieve both the bytes correctly on the serial port as 0x55.

If not then, does it recieve 'b'. If yes then there is definitely a problem with the chip. There are other ways to find this problem. We will get into this after you complete these tests.

If you get something else, then maybe the data is changing between the time the data is read and before you actually use it. Then one obvious doubt raised is that: Was there any interrupt during this time? Then it will 99% damage the data. Try by disabling the interrupts and check the result.

Bye,
Mr. Kiran V. Sutar.