External Direct

External Memory is accessed using a suite of instructions which use what I call "External Direct" addressing. Ii is called called this because it appears to be direct addressing, but it is used to access external memory rather than internal memory.
There are only two commands that use External Direct addressing mode:
MOVX A, @DPTR
MOVX @DPTR, A
As you can see, both commands utilize DPTR. In these instructions, DPTR must first be loaded with the address of external memory that you wish to read or write. Once DPTR holds the correct external memory address, the first command will move the contents of that external memory address into the Accumulator. The second command will do the opposite: it will allow you to write the value of the Accumulator to the external memory address pointed to by DPTR.

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