Hallo Pravin,

can you read the RAM? Means, are there !RD pulses, when you read the RAM?
May be, you destroyed NMOS output transistor of port pin during experimenting by an accidental short circuit of !WR port pin to Vcc? Then, micro would never again be able to deliver low level here.

You can test it, by exchanging your micro with a new one.

Good luck,
Kai