My gosh you go through a huge hullabalu to increment the 16-bit value in R6::R7. Why it even necessary to involve the B register?

Here is the straight forward way to increment R6::R7 where R6 is the most significant byte...

;
;to increment R6::R7 do this
;
INC_R6R7:
    INC   R7
    MOV   A, R7
    JNZ   LOC_A
    INC   R6
LOC_A:
    ...

And a way to decrement R6::R7 where R6 is the most significant byte...should you be interested

;
;to decrement R6::R7 do this
;
DEC_R6R7:
    MOV   A, R7
    DEC   R7
    JNZ   LOC_B
    DEC   R6
LOC_B:
    ...

Michael Karas