Is there any use of the XTHL instruction in an 8085 microprocessor?

Question

I understand what XTHL does, but can someone give an example of a scenario where one would actually use it? Moreover, if possible please share the code for the application as well.

Answer 1

One use includes passing arguments to assembly functions like this:

    CALL function_name
    DB   1,2,3 ;arguments
...
function_name:
    XTHL
    MOV A,M ;get argument
    INX H ;move to next argument
    ...
    XTHL ;now return modified return address to stack,
         ;also restoring HL contents as well

Other use is to have shadow copy of HL on top of stack, for example:

    DAD   B ;hl=hl+bc
    XTHL  ;'shadow' hl swapped in
    JNC   no_inc
    INX   H
no_inc:
    DAD   D ;hl=hl+de
    XTHL
    ;so we just added 32-bit number in DE:BC to HL:(TOS)

In similar way you juggle words that are pushed on the stack.

Some abuse also includes this:

    LXI SP,addr1
    XTHL
    LXI SP,addr2
    XTHL
    ...

this code will move chain of data words through locations pointed by consecutive LXI SP,addr commands. Of course, this requires interrupts disabling, but gain is speed.