You can access - read and write - internal data memory using the DBY operator. For example, copying a byte from address 0D0h into a BASIC variable X is as simple as 10 X = DBY(0D0h), and writing say 23 decimal into the same location is 20 DBY(0D0h)=23.

However, I see no merit in accessing SFRs like the accumulator - its contents gets immediately clogged by the interpreter itself. Also, for accessing the "useful" SFRs, such as the timer control registers, or the interrupt enable/priority registers, there are builtin operators in BASIC52 itself - see again abovementioned chapter 7 of the original manual.

JW