code working in simulator but not when burnt.

The flash memory can not be used instead of RAM. It is intended for code but you can instruct the compiler to place constants there too. But it is a type of read-only memory, so if you need to be able to regularly change the value of a variable then you need to look at something else.

DATA in this situation is one of several memory areas in your processor. The different memory areas in the processor has different capabilities, and requires different ways to access them. The DATA area is a RAM area built into the 8051 chip. The XDATA is another memory area, originally intended for use with extermal memory chips and requiring different processor instructions to access the variables. The 8051 can have internal and/or external XDATA memory. The DATA area is extremely limited in size, but it is possible to have very large XDATA support. The instruction set is intended for accessing up to 64kB of XDATA, but it is possible to get past this limit. People who think that 64kB of XDATA is little should probably look at other processor architectures instead.

You can use the following link and search for 8051 chips with enough space for your program and for your variables.
http://www.keil.com/dd/search_parm.asp

Note that the colum for RAM has the heading "DATA
+XDATA", giving the built-in amount of RAM for these two memory areas.

For configurations that are seldom changed, but must be remembered after a power loss, you can look at the column "On-chip EEPROM". But you are limited to 100.000 to 1000.000 writes/memory cell for most EEPROM, so it is a complement, but not suitable to use instead of RAM.

The flash memory can not be used instead of RAM. It is intended for code but you can instruct the compiler to place constants there too. But it is a type of read-only memory, so if you need to be able to regularly change the value of a variable then you need to look at something else.

DATA in this situation is one of several memory areas in your processor. The different memory areas in the processor has different capabilities, and requires different ways to access them. The DATA area is a RAM area built into the 8051 chip. The XDATA is another memory area, originally intended for use with extermal memory chips and requiring different processor instructions to access the variables. The 8051 can have internal and/or external XDATA memory. The DATA area is extremely limited in size, but it is possible to have very large XDATA support. The instruction set is intended for accessing up to 64kB of XDATA, but it is possible to get past this limit. People who think that 64kB of XDATA is little should probably look at other processor architectures instead.

You can use the following link and search for 8051 chips with enough space for your program and for your variables.
http://www.keil.com/dd/search_parm.asp

Note that the colum for RAM has the heading "DATA
+XDATA", giving the built-in amount of RAM for these two memory areas.

For configurations that are seldom changed, but must be remembered after a power loss, you can look at the column "On-chip EEPROM". But you are limited to 100.000 to 1000.000 writes/memory cell for most EEPROM, so it is a complement, but not suitable to use instead of RAM.

Thanks PER for that information..