Pravin:

Have you hooked up an oscilloscope to the interface lines and checked to see if the hardware interface to the RAM chip is operating correctly? This thread is beginning to sound more and more like you have some type of interface problem.

If you have not yet performed the oscilloscope routine then you only need two small programs at this point. One to write one location in a loop and another to read one location in a loop. Use these to verify the timing according to data sheets, check the power connections, and ensure that things are clean and noise and glitch free. You can vary the address accessed via several different versions of the program to check to make sure the right address bits at the right levels get to the correct pins of the RAM chip. You can then vary the data bit values on the write version of the test program to validate the data connections.

It is my impression that in your "manually switching the RD/ line" that you have not looked at the hardware connections in real detail.

Michael Karas