MOV in ASM

If my ASM code is previously coded to run for 256 byte internal RAM of MCU (use MOV instruction) and i now need to change to external 2Kbyte RAM (use MOVX), then should i change R7 to R7:R6 because R7 is not big enought to address BUFFER? or can anyone suggest what should i change the following code?

Some 8051 family variants have extra memory beyond the 256 byte scratchpad RAM that is described as "internal". Invariably, a better description from a programmers point of view would be "external on-chip RAM". To the CPU this extra on-chip RAM looks just like RAM that would be in an external chip accessed via an external bus on a conventional 8051/8052 design. Of course, there will be some other differences, P0 may be available as an I/O port for example.

So, you need to use a MOVX instruction to get at this on-chip ram. For example, you will need something like the following (untested):

unsigned char Test( unsigned int address )
{
    address = address; //suppress UNUSED warning
                       // will be optimised out.

    #pragma asm

        MOV     DPH,R6
        MOV     DPL,R7
        MOVX    A,@DPTR
        MOV     R7,A
        RET

    #pragma endasm

    return( 1 );       // dummy return
}

If my ASM code is previously coded to run for 256 byte internal RAM of MCU (use MOV instruction) and i now need to change to external 2Kbyte RAM (use MOVX), then should i change R7 to R7:R6 because R7 is not big enought to address BUFFER? or can anyone suggest what should i change the following code?

Some 8051 family variants have extra memory beyond the 256 byte scratchpad RAM that is described as "internal". Invariably, a better description from a programmers point of view would be "external on-chip RAM". To the CPU this extra on-chip RAM looks just like RAM that would be in an external chip accessed via an external bus on a conventional 8051/8052 design. Of course, there will be some other differences, P0 may be available as an I/O port for example.

So, you need to use a MOVX instruction to get at this on-chip ram. For example, you will need something like the following (untested):

unsigned char Test( unsigned int address )
{
    address = address; //suppress UNUSED warning
                       // will be optimised out.

    #pragma asm

        MOV     DPH,R6
        MOV     DPL,R7
        MOVX    A,@DPTR
        MOV     R7,A
        RET

    #pragma endasm

    return( 1 );       // dummy return
}