Apple II User Manual

     EXAMPLE:

     14 34 A0   SET  R4   $A034     ;Init pointers

     15 22 90   SET  R5   $9022

     84         POP  @R4            ;Move byte from

     95         STP  @R5            ;$A033 to $9021

     84         POP  @R4            ;Move byte from

     95         STP  @R5            ;$A032 to $9020

ADD:

     ADD Rn              [ An ]

     The contents of Rn are added to the contents of ACC (R0),

     and the low-order 16 bits of the sum restored in ACC. the

     17th sum bit becomes the carry and the other branch

     conditions reflect the final ACC contents.

     EXAMPLE:

     10 34 76   SET  R0   $7634     ;Init R0 (ACC) and R1

     11 27 42   SET  R1   $4227

     A1         ADD  R1             ;Add R1 (sum=B85B, C clear)

     A0         ADD  R0             ;Double ACC (R0) to $70B6

                                    ;with carry set.

SUBTRACT:

     SUB Rn              [ Bn ]

     The contents of Rn are subtracted from the ACC contents by

     performing a two's complement addition:

     ACC = ACC + Rn + 1

     The low order 16 bits of the subtraction are restored in the

     ACC, the 17th sum bit becomes the carry and other branch

     conditions reflect the final ACC contents. If the 16-bit

     unsigned ACC contents are greater than or equal to the 16-bit

     unsigned Rn contents, then the carry is set, otherwise it is

     cleared. Rn is not disturbed.

     EXAMPLE:

     10 34 76   SET  R0   $7634     ;Init R0 (ACC)

     11 27 42   SET  R1   $4227     ;and R1

     B1         SUB  R1             ;subtract R1

                                    ;(diff=$340D with c set)

     B0         SUB  R0             ;clears ACC. (R0)

POP DOUBLE-BYTE INDIRECT:

     POPD @Rn            [ Cn ]

     Rn is decremented by 1 and the high-order ACC byte is loaded