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First let me start off by saying this will eventually cover 3 distinct upgrades, with the first one being what is called the ARROW2JOY-XLD. As the name implies this is meant for use with a 1088XLD. So what's this all about? Well first let me tell you a small story (I promise I'll keep it short and sweet). I was looking at the various Atari 8-bit emulators the other day, and noticed that one in-particular supported a joystick mode via the arrow keys on the keyboard. My first reaction was "Hey that's Cool!", and so it began. Now how could I do something like that with the TK-II hardware? Well it turns out I first had to steal a page from the AKI (Atari Keyboard Interface). The AKI syncs up with the Pokey chip on the Atari using only 2 bits of Pokey's 6-bit key scan counter and then builds a copy in software running inside the PIC chip that drives it. In retrospect my design was using all 6-bits of the Pokey counter as a reference. So in order for me to free up some I/O for other uses (i.e., Joystick mode), I decided to mimic what the AKI was doing. This freed up four I/O lines which I was able to decode into 9 states. That being JOY-Up, JOY-Down, JOY-Left, JOY-Right, Aux1, Aux2, Aux3, standby (IDLE), and finally JOY-Trigger. The trigger function had to be kept separate, so that it could be initiated independently of direction. Since I was addressing a 74LS156 decoder with 3 of the I/O lines, that gave me 8 possible decoded outputs, with one as I already mentioned being a 'do nothing' state. So as part of the decode process I automatically got 3 extra outputs beyond the 4 direction bits I required, which I called AUX 1-3. I decided to terminate these 3 outputs on an independent 3-pin header. They are open collector and momentary in nature, so would work fine for something like a disk swap button, something the XLD already has implemented for its built-in IDE. Anyway they were free, and are available for whatever the user wants. Getting back to the Joystick aspect, here is how that's been applied in a new version of the TK-II firmware (V2.5J). Basic Keyboard Commands PS/2 ALT+J toggles into and out of the Joystick Mode* PS/2 Arrow Keys produce Joystick X/Y direction switching PS/2 Left-Windows Key = Joystick Trigger Button PS/2 ALT+1-3 = AUX outputs 1-3 *Note: The Joystick Mode is volatile, and will go back to the arrows navigation mode (default) on a power cycle. So here's what the new TK-II piggyback upgrade board looks like (plugs right into the TK-II chip socket on the 1088XLD motherboard). And it has a small companion interface board to connect up with the joystick signals on the 1088XLD. Here's the complete system in use. There were other changes in the 2.5J TK-II firmware which will need to be documented, and there is a new version coming of the TK-II Pokey piggyback board for use in standard Atari systems that will integrate the joystick functions. So stay tuned for more info to come . Please visit my website at: https://ataribits.weebly.com/arrow2joy-xld.html
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