The Apple II took a significant amount of CPU time to read the joystick's resistive inputs and they had to be read several times in succession to obtain an accurate position of the stick. While this was potentially compatible with any Apple II game which supported a standard joystick, some games had really picky joystick input routines and required more than the three levels of resistance per axis this adapter provided. This was essentially the Gravis Gamepad approach in the IBM PCs. Inside the device was a chip and circuitry which set a position on the joystick, when pushed, to a resistance level. This is a black box with two DE-9 input ports for Atari 2600-style digital controllers and a 16-pin ribbon cable to connect to the Apple II's Game I/O Socket. Early IBM PC software could rely on the general speed of a 4.77MHz 8088 CPU found in the IBM PC and IBM PC/XT, but that would be challenged by slower (IBM PCjr) and increasingly faster systems (IBM PC AT) as time went on. CPU accelerators were available for the Apple II, and the Apple IIc+ and the IIgs can accelerate 8-bit software, but the expectation remained 1MHz for timing sensitive tasks like sound output, disk drive access and joystick reads. The Apple II was generally fixed at 1MHz operation for most of its operational life and virtually every joystick-supporting piece of software for the Apple II expects joystick reads to occur at 1MHz. When pressed Apple push buttons give a logic 1 and IBM buttons give a logic 0. Apple joysticks also drive pushbutton inputs low to ground via a 560Ohm resistors in the joystick when not pressed, which will pose some challenges that the IBM PC Joysticks, which drive the button inputs high when not pressed on the interface card, do not. The IBM PC supported a nearly-identical joystick interface, adding support for a 4th button and using 100KOhm variable resistors in place of the 150KOhm variable resistors Apple specified. The connector also loses two resistive inputs and one pushbutton input. The IIc's 9-pin connector doubles for the mouse port, but when a mouse is plugged in, the signals for the mouse movement and direction bypass the timer chip. The Apple IIe, IIc and IIgs also have 9-pin connectors which provide the resistive input and pushbutton input signals, but nothing else. Finally, there is a strobe output which drives the line low for a CPU clock cycle when accessed. There are also four digital 1-bit toggled outputs, called annunciators. There are three digital 1-bit inputs, intended for pushbuttons. Each input is intended to be connected to a variable resistor, which completes the circuit which goes to the inputs on the 558 timer chips. On the II and II+, the input for a joystick, paddle or a device alternate to the keyboard was a 16-pin DIP socket on the mainboard. The Apple II was a bit old-fashioned when it came to connecting things like paddles or joysticks to the machine. This article will give an overview of attempts both old and new. When it became a retro-computing machine, there have been a few more homebrew hardware efforts to bring digital input to older games. During the Apple II's commercial life, there were a few attempts to bring digital joystick support to the computer. Other home computers and consoles used digital joysticks, which were often better for single-screen games than analog devices. The Apple II had thousands of games released during its long life-span, and from its first game, Breakout (later known as "Brick Out" and "Little Brick Out"), many of them used analog controllers like paddles and joysticks.
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