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Seeking a sanity check on a couple 800XL modifications.


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Firstly, "Hi, I'm new." Grew up with a 5200, played plenty of 2600 games over the years, but my recently acquired 800XL is my first step into Atari's micros. I've got several ideas I'd like to run past the collective just to make sure I'm not missing something obvious.


I'd like to internalize the SIO2PC. I've got one of those $9 CHIP computers that I think would be well-suited to the task. I know I'll need a level converter to talk to its 3.3V UART. Since I'll be wiring the XL for S-Video output, I'm thinking of hooking the CHIP's composite output to the appropriate pin on the monitor output so that I can just swap inputs on the display to view it. It's got 4GB of integrated storage and WiFi/BT, so physical access isn't a priority. For power, the plan is to tap into the XL's input before the switch and maybe hide a small toggle in the case vents so that I can power up the CHIP first and keep it on between reboots. I've got one of the heavy, epoxy-filled PSUs for the Atari, which seem to have a poor reputation anyway, so I don't mind building a new supply for the extra load, probably something like 5V/3A. I haven't plotted out free space inside the case yet, but I might even consider moving the power supply inside, too, and just sticking a figure-8 plug on the back.


Got some possible cosmetic mods bouncing around in my head, too. While I don't mind the classic look, I'm thinking of painting the case black and getting a laser-cut aluminum sheet to put across the top part, around the cart slot, bringing it more in line with the 5200/7800 aesthetic. Further along that line of thought, maybe cut an Atari logo into the sheet and throw some RGB LEDs under it to recreate that lovely rainbow logo used for many of the boot screens. Could also serve as an access indicator for the SIO interface. Going really pie-in-the-sky, it might be interesting to integrate a small touchpad on the top panel for navigating RespeQT, eliminating the need for an external mouse.




1. Any obvious flaws in this?


2. How does the SIO daisy-chaining work? If I wire up the internal interface directly to the PCB or the back of the jack, will additional external devices still work normally, or are there extra components or such required?


3. Are the spring-loaded card edge covers on the cartridges not the coolest thing ever?

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The best SIO2PC interface IMO is the one that fits inside a SIO plug and has the USB plug coming out the back. Still allows daisy chaining with most devices so long as the peripheral has 2 sockets and allows the +5V passthru.


One of my 130XEs I built in the SIO2PC and just soldered the connections to the internal leads going to the stock SIO socket. The only issue here is that I've also taken power to the chip from the SIO plug which means less power is available if anything downstream needs to use it. Generally though, the +5 power on SIO isn't used at all, but can be utilized by peripherals to know if the computer has just powered up.


Daisy chaining works as each device with 2 sockets allows the signals to pass through. All devices listen to data on the serial bus when /Command goes low. The device ID for a SIO operation is contained in the Command Frame. Once the command frame is complete, any non involved device should simply go idle and wait for the next /Command sequence. Obviously this only works properly when all devices have a unique ID (ie, not allowed to have 2 disk drives set to save drive #)


Exception to both the above - the cassette drive. For whatever reason the tape drive in fact uses the +5 volts from the computer to drive part of it's circuitry. Also daisy chaining isn't possible with the 410 tape drive as it's got the single tethered SIO plug only. Tape drives also differ from other SIO devices in that there's no comms protocol or ID in use. The only control from the computer side is to allow the motor to operate or not in Play/Rec mode. Nothing to tell the computer if a tape drive is present or not. In theory multiple tape drives could be used so long as at least one has a passthru.


The spring loaded dust cover types used in early Atari carts are cool, not used later probably due to penny pinching.

Edited by Rybags
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