Hi Chang,

you must first read the manual of your evaluation board very carefully. Sometimes its very tricky designed to support program download, since this not supported by the standard 8051 core (program memory = read only).
So its also suggest to read the 8051 data sheet to understand external memory addressing.

There are 2 methods known to start code from download:

1.
On address 0x0000 was a boat loader and your application must start something above, e.g. at 0x4000.

2.
There is some logic on board, which allow to switch off the boot loader and place the RAM (Flash) with your application on address 0x0000.
This was typically done with writing to a reserved address in the XDATA space.
Watch, that the application never touch these addresses !


Also use LARGE model only if really needed. Typically this double the program size and reduce execution speed to about 50 ... 10%.
Also if LARGE used, you must first tell how many external SRAM connected and on which address it started.
So, if your program in RAM at address 0x0000 and you tell the compiler not another range as data space, then it place data also on 0x0000 and destroy the code !


Peter