The 7800 eXpansion Module
What is the 7800XM?
The 7800 XM (eXpansion Module) is a plug in device that is installed into the top cartridge slot of any Atari 7800 console. Once installed this intelligent device will detect whether Atari 2600 or Atari 7800 cartridges are installed into it. If an Atari 2600 cartridge is install, the Atari 7800XM goes into a disabled mode so it just acts as a pass through device and does not interfere with Atari 2600 cartridges and their functions. If an Atari 7800 compatible cartridge is installed into it, it will check the cartridge and detect if it is PAL or NTSC and then it will check if it has an onboard POKEY chip. Depending on the type of cartridge and whether it is equipped with its own onboard POKEY chip, the 7800XM will configure itself accordingly to work with that type of game.
What features does the 7800XM have?
The 7800XM was designed to be a device that could've been made in the 1984-1992 era by Atari, so it only uses devices that could've existed at the time to keep the console as true to form as possible.
The 7800XM comes with onboard High Score keeping, a design which was originally done by GCC (the designers of the 7800) but this feature was canceled when the Atari 7800 was released. 9 of the original 10 games that GCC wrote for Atari have high score keeping functions built into them so they automatically work with this feature. Numerous homebrew games have also been released with high score keeping code in them, so they too work with this feature.
The 7800XM also has 128K of onboard, game usable memory to greatly enhance and improve games that will be written to take advantage of this additional memory.
The 7800XM has an onboard POKEY audio processor chip, giving games the same high quality 4 channel sounds that the Atari computers and Atari 5200 enjoy. Many games have already been coded to use the POKEY chip when detected, so they will automatically use this audio processor when they are plugged into the XM. Also the XM can detect is a cartridge, such as Ball Blazer, already has an onboard POKEY chip inside of it and the XM will then disable its own POKEY chip and just pass through the audio from the POKEY chip in the cartridge.
Another feature from the POKEY chip in the XM is it is connected to a 15 pin keyboard port that is Atari XEGS keyboard compatible. This will allow more complex games with keyboard input to use a keyboard for game play. Michael St. Pierre, the famous designer of the TransKey interface that allowed IBM keyboards to be used on Atari home computers has released a plug in interface for the XEGS port that allows IBM PC keyboards to work, this has been tested with the 7800XM and is 100% compatible.
With the 7800XM you get not one, but two audio processors. A Yamaha 2151 audio synthesiser chip is also onboard the 7800XM. This chip was used in several Atari coin-op games such as Marble Madness and the quality of the audio from this chip is truly breath taking. The possibilities of releasing Atari 7800 games with audio from this chip will completely change the way people view the Atari 7800.
The 7800XM also has an SIO port, it is connected to the POKEY chip and has basic functions, to give the 7800XM full SIO peripheral capabilities there is a footprint inside of the 7800XM where hardware hackers and modders can add a PIA or can experiment and try expanding the 7800XM's capabilities even further.
Is the 7800XM hard to install? What tools do I need?
The 7800XM is an easy to install as plugging a cartridge into your Atari 7800, it just plugged right on top, no tools, soldering or any modifications to the 7800 console. Just plug and play.
Does the 7800XM make all of my existing games better?
No, the existing games do not change, only games that have code in them to access features of the 7800XM will become more enhanced. Some current games play regular Atari 2600 audio, but have code that if they detect a POKEY chip, they play all their sounds in POKEY audio. Games that have high score code play normal, but when they detect High Score keeping, they bring up a high score save screen and a list of the latest high scores. Other games may be XM only games because they may be coded to only work with the XM RAM or other features, so you will have to check with the home brewer and read the information on a 7800 game to make sure that it isn't an XM ONLY game.
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