Thank you Valentin and Jan for your suggestions .
I have replaced 80C51 with AT89C51RD2 but its not working.
Board is configured for external RAM and external program memory ( EA pin is grounded ).
I checked datasheet AT89C51RD2 it says :

"
One bit of the HSB, the BLJB bit, is used to force the boot address:
• When this bit is programmed (‘1’ value) the boot address is 0000h.
• When this bit is unprogrammed (‘1’ value) the boot address is F800h. By default,
this bit is unprogrammed and the ISP is enabled.
"

I don't have programmer ,so could not program the Hardware Security Byte (HSB) . But by default, code should execute from memory location F800h. I wrote a small programm to toggle port1 pin and placed it at memory location 0xF800 inside EEPROM. I'm not getting any signal at port1 pin.
Here is my source code :

...insert code here
 

org 0h
ljmp isp_boot
org 0100h
my_start:
setb P1.0
setb P1.1
setb P1.2
setb P1.3
clr P1.0
clr P1.1
clr P1.2
clr P1.3
sjmp my_start
org 0f800h
isp_boot:
ljmp my_start
end


Any suggestion to resolve the issue ?

Thanks
Sanjay