Mr Oleg
your idea was nice but the problem in mycase is that both my INT lines are also in use. one for the keyboard and another to detect and read some 8 interrupt generators.
i am using PAL22v10 to generate the interrupt and give an encoded value on P1. would you be kind enough to let your ideas soar a little more to help me out.


Mr Erik
sir i am sorry but i couldn't comprehend the message or remarks sent by you correctly.
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.. not available in local market i guess ...

also please through some more light on backup to sram through diodes and the battery.. if possible a simple diagram will help

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 .....
please help me more.

Mr Rustu kaya
your input along with your experimentations were really enlightening... 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 ....


still looking out for more help
regards
nitin