The subroutine establishes a call frame using register A6 as the frame pointer. This kind of calling convention supports reentrant and recursive code and is typically used by languages like C and C++. The subroutine then retrieves the parameters passed to it ( and ) from the stack. It then loops, reading an ASCII character (one byte) from the string, checking whether it is a capital alphabetic character, and if so, converting it into a lower-case character, otherwise leaving it as it is, then writing the character into the string. Finally, it checks whether the character was a null character; if not, it repeats the loop, otherwise it restores the previous stack frame (and A6 register) and returns. Note that the string pointers (registers A0 and A1) are auto-incremented in each iteration of the loop.