LPC , CGA , PCA ??? are these the different variants of Processors available for example 89LPC51 or something of that sort. because i have never heard of them..
evidently you have heard of the 89LPCxxx which has a CGA or whatever they call the PCA type function inside. For some reason the name is different from Programmable Counter Array in the LPC series. The 87LPC is even cheaper, but OTP.

also please through some more light on backup to sram through diodes and the battery.. if possible a simple diagram will help
Put on your thinking cap. 2 diodes with the cathodes connected.

regarding your other help ... dallas IC's dual resets ..if i am not wrong they are known as NVRAM control IC's but sir all those will add to my cost which i have keep the mare minimum .....
what good will it do to keep cost down if you lose your memory.

but i am in requirement of 32K RAM and so for the time being i can't use the internal RAM .. at our place bangalore in india 89c51 4K variant is available for Rs 80 ... 2USD approx and 89c51RD2 64K with 1K SRAM is available for Rs 275 nearly 6USD so u see the obvious choice is 89c51 with 62128/62256 outside ....
thanks for your kind concern ....
This does not make sense, You speak of 32k RAM and compare the flash size of the chips.

Erik