30A

41

 

MLOOP

LD

@R1

;R1 holds source

30B

52

 

 

ST

@R2

;R2 holds dest. addr.

30C

F3

 

 

DCR

R3

;Decr. length

30D

07

FB

 

BNZ

MLOOP

;Loop until done

30F

00

 

 

RTN

 

;Return to 6502 mode.

310

C9

C5

NOMOVE

CMP

#"E"

;"E" char?

312

D0

13

 

BEQ

EXIT

;Yes, exit

314

C8

 

 

INY

 

;No, cont.

NOTE: Registers A, X, Y, P, and S are not disturbed by SWEET 16.

Instruction Descriptions:

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

The SWEET 16 opcode listing is short and uncomplicated. Excepting relative branch displacements, hand assembly is trivial. All register opcodes are formed by combining two Hex digits, one for the opcode and one to specify a register. For example, opcodes 15 and 45 both specify register R5 while codes 23, 27, and 29 are all ST ops. Most register ops are assigned in complementary pairs to facilitate remembering them. Therefore, LD ans ST are opcodes 2N and 3N respectively, while LD @ and ST @ are codes 4N and 5N.

Opcodes 0 to C (Hex) are assigned to the thirteen non-register ops. Except for RTN (opcode 0), BK (0A), and RS (0B), the non register ops are 6502 style branches. The second byte of a branch instruction contains a +/-127 byte displacement value (in two's complement form) relative to the address of the instruction immediately following the branch.

If a specified branch condition is met by the prior register op result, the displacement is added to the PC effecting a branch. Except for the BR (Branch always) and BS (Branch to a Subroutine), the branch opcodes are assigned in complementary pairs, rendering them easily remembered for hand coding. For example, Branch if Plus and Branch if Minus are opcodes 4 and 5 while Branch if Zero and Branch if NonZero are opcodes 6 and 7.

SWEET 16 Opcode Summary:

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

Register OPS-

 

 

 

1n

SET

Rn

Constant (Set)

2n

LD

Rn

(Load)

3n

ST

Rn

(Store)

4n

LD

@Rn

(Load Indirect)

5n

ST

@Rn

(Store Indirect)

6n

LDD

@Rn

(Load Double Indirect)

7n

STD

@Rn

(Store Double Indirect)

8n

POP

@Rn

(Pop Indirect)

9n

STP

@Rn

(Store POP Indirect)

An

ADD

Rn

(Add)

Bn

SUB

Rn

(Sub)

Cn

POPD

@Rn

(Pop Double Indirect)

Dn

CPR

Rn

(Compare)

 

 

 

 

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Image 44
Apple II manual Dcr, BNZ Mloop, Rtn, Nomove CMP, BEQ Exit, Iny, Set, Ldd, Std, Stp, Add, Sub, Popd, Cpr
Page 43 Page 45

II specifications

The Apple II, launched in April 1977, was one of the first highly successful mass-produced microcomputer products. It marked a significant leap in personal computing, setting standards for future developments in the industry. Created by Steve Wozniak and Steve Jobs, the Apple II differentiated itself with its user-friendly design, appealing aesthetics, and robust capabilities.

One of the standout features of the Apple II was its open architecture, which allowed users to expand and enhance the computer's functionality. This design enabled hundreds of third-party hardware and software developers to contribute to its ecosystem, resulting in an array of peripherals, including printers, modems, and storage devices. The Apple II utilized a MOS Technology 6502 microprocessor running at a clock speed of 1 MHz. Initially equipped with 4 KB of RAM, the machine could be expanded to 48 KB, accommodating more complex applications and programs.

The Apple II was also notable for its colorful graphics. It was one of the first computers to support color display, offering a 6-color palette with a resolution of 280x192 pixels in 16 colors when using its Color Graphics Card. This feature significantly enhanced the visual appeal of games and educational software developed for the platform, making computing more accessible and entertaining for various audiences.

Apple's commitment to user experience was evident in the design of the machine. It featured an integrated keyboard and a plastic case, which was both durable and visually appealing. The self-contained design included drive bays for floppy disk drives, allowing for quicker data access than traditional tape drives. It also supported audio output, enabling sound effects and music, a novelty at the time.

The introduction of the Apple DOS operating system further underscored the machine's capabilities. DOS streamlined file management and made it easier for users to navigate and manage their data. The combination of hardware and software positioned the Apple II as an educational tool and a gaming platform, fostering a vibrant software ecosystem.

The Apple II family continued to evolve, with variations like the Apple II+, IIe, and IIgs being introduced over the years. These iterations brought enhancements in memory, processing power, and graphics capabilities. The legacy of the Apple II endures, not only as a foundational product in personal computing but also as a symbol of innovation that paved the way for future advancements in technology. Its impact is still felt today, as it inspired countless developers and shaped the trajectory of the computer industry.
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