Load function in assembly

Can you clarify your question? Do you mean that you want to call a function in assembly language when you only have the address of the function to be called stored in a variable or registers?

It is possible to use something like the (untested) code below. Basicly, the return address and the function pointer are loaded onto the stack and then a RET instruction causes the CPU to pop the address of the function pointer into the PC. When the function executes a RET, the return address will be popped into the PC and the CPU will be back at return_address.

    MOV     A,#LOW(return_address)
    PUSH    Acc
    MOV     A,#HIGH(return_address)
    PUSH    Acc
    MOV     A,function_pointer_low
    PUSH    Acc
    MOV     A,function_pointer_high
    PUSH    Acc
    RET
retern_address:
    ....

whether it is possible to load the function with its address?

Your terminology is somewhat strange. What you're doing here is usually referred as "calling" a function", not "loading" it.

That set aside, it's completely unclear what it is you want to do. Note that _function is the address of that function, effectively --- _function is just a more convenient way the assembler and tools allow you to write it.

Basicly, the return address and the function pointer are loaded onto the stack and then a RET instruction causes the CPU to pop the address of the function pointer into the PC.

That technique has no excuse being used on the 8051, which has a perfectly fine "computed goto" instruction:

       JMP @A+DPTR

Hi,
what is a problem?

CALL function_address

 CALL 0x1234

Hi,
Sometimes it needs to keep DPTR unmodified, for example, if you pass a parameter to called function via DPTR. So the usage of "call-via-stack" method is still usable with C51.

Regards,
Oleg

Thank you all for your replies.

To clarify my question, what I needed to do was to call a function whose address is stored in variables.

Anyway, as suggested, I have tried by loading the return address and the function onto the stack and it is working fine.

Thank you.