Branch if Minus ONE, Branch if not Minus ONE, Break

BRANCH IF MINUS ONE

BM1 ea

[ 08 d ]

A branch is effected only if the prior 'result' was minus one ($FFFF Hex). Branch conditions are not changed.

BRANCH IF NOT MINUS ONE

BNM1 ea

[ 09 d ]

A branch effected only if the prior 'result' was not minus 1.

Branch conditions are not changed.

BREAK:

[ 0A ]

A 6502 BRK (break) instruction is executed. SWEET 16 may be re-entered non destructively at SW16d after correcting the stack pointer to its value prior to executing the BRK.

RETURN FROM SWEET 16 SUBROUTINE:

[ 0B ]

RS terminates execution of a SWEET 16 subroutine and returns to the SWEET 16 calling program which resumes execution (in SWEET 16 mode). R12, which is the SWEET 16 subroutine return stack pointer, is decremented twice. Branch conditions are not changed.

BRANCH TO SWEET 16 SUBROUTINE:

BS ea

[ 0c d ]

A branch to the effective address (PC + 2 + d) is taken and execution is resumed in SWEET 16 mode. The current PC is pushed onto a SWEET 16 subroutine return address stack whose pointer is R12, and R12 is incremented by 2. The carry is cleared and branch conditions set to indicate the current ACC contents.

EXAMPLE: (Calling a 'memory move' subroutine to move A034-A03B to 3000-3007)

15	34	A0		SET	R5	$A034	;Init pointer 1
14	3B	A0		SET	R4	$A03B	;Init limit 1
16	00	30		SET	R6	$3000	;Init pointer 2
0C	15			BS	MOVE		;Call move subroutine
45			MOVE	LD	@R5		;Move one
56				ST	@R6		;byte
24				LD	R4
D5				CPR	R5		;Test if done
04	FA			BP	MOVE
0B				RS			;Return

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.

Apple II Branch if Minus ONE, Branch if not Minus ONE, Break, Return from Sweet 16 Subroutine

Models: II