Indexed addressing:

Write a subroutine named "Copy" to implement the following flowchart.

Your subroutine needs to start with the label "copy:" so that an assembler can call it correctly. Your subroutine needs to preserve all registers at the beginning and then restore all registers just before it exits. $($Hint: You not only need to save R$20,$ you also need to save registers X and Y$.$ They need to be saved $8$ bits at a time, using XH$,$ XL$,$ YH$,$ and YL$.)$ Note that the "preserve" and "restore" steps are not shown in the flowchart $-$ you need to figure out where to add them.