Apple II User Manual

VN DSP NVA DATA DATA Terminator

The SWEET 16 registers are as shown:

low high low high low high low high

$0000 1E 00 08 08 08 0A 00 00

---------- ---------- ---------- ----------

| | | |

R0 R1 R2 R3

(acc) (source) (dest) (#bytes)

The low order byte of R0, the SWEET 16 accumulator, has $1E

in it, the last byte moved (the 8th).

The low order byte of the source register R1 started as $00

and was incremented eight times, once for each byte of moved

data.

The high order byte of the destination register R2 contains

$0A, which was entered at 10 (the variable) and poked into

the SWEET 16 code. The low-order byte of R2 was incremented

exactly like R1.

Finally, register R3, the register that stores the number of

bytes to be moved, has been poked to 8 (the variable B) and

decremented eight times as each byte got moved, ending up

$0000.

By entering character strings and varying the number of bytes

to be moved, the SWEET 16 registers can be observed and the

contents predicted.

Working with this demonstration program, and study of the

text material will enable you to write SWEET 16 programs that

perform additional 16 bit manipulations. The unassigned

opcodes mentioned in the "WOZ Dream Machine" article should

present a most interesting opportunity to "play".

SWEET 16 as a language - or tool - opens a new direction to

Apple ][ owners without spending a dime, and it's been there

all the time.

"Apple-ites" who desire to learn machine language programming,

can use SWEET 16 as a starting point. With this text

material to use, and less opcodes to learn, a user can

quickly be effective.

Listing #1

>List

10 PRINT "[D]BLOAD SWEET": REM CTRL D

20 CALL - 936: DIM A $ (10)

30 INPUT "ENTER STRING A $ " , A $