Atari XL/XE-series Technical Details and Trivia


  • SIO (Serial Input/Output) interface

Technical Facts

  • There was graphics mode called APAC (Any Point, Any Color-from 256 choices) "mode" which allows for 256 colors by alternating modes 10 and 11 on every line, and it can also be interlaced to double the vertical resolution; 80x96&80x192
  • The 1200XL came with a built-in self test, which was a novel feature of the time (before computers had a "BIOS").




  • The "GTIA bug" which many people refer to is usually referring to the fact that Graphics 10 pixels are drawn half a pixel to the right (probably delay thanks to having to access the palette?). This is utilized in HIP/RIP/TIP modes, the trick is to have 2 screens defined - one with mode 10 on even lines, the other with odd - Graphics 9 is usually used on the other lines.
  • Hardly anyone made use of the extra modes the GTIA chip offered - Lucasfilm Games were among the first back in 1983 with Jaggi Lines.
  • The original design of the 1000X had a PBI (peripheral bus interface) expansion connector, but this was left out of the 1200XL leaving it to rely entirely on the SIO (serial input/output) interface instead which dated back to the Atari 400/800. Unfortunately, the +12V line of the SIO interface was left unconnected, so only 5V power was available for devices connecting through this!
  • Another faux-pas of the 1200XL was that the video circuitry provided more chroma (to provide a more colourful image), but the chroma signal line was not connected to the monitor port, so nothing could make use of it