XM expansion

Hardware entity

An homebrew expansion module


The first video game about XM expansion was released in 1987.

AtariAge and Atari has published most of these games

Hardware features include:
(D)Games can be developed that use XM features but also work (without said features) on a stock 7800.
(C)Works with 2600 and 7800 games (possible to overcome compatibility issues for certain 2600 games)
(K)XEGS keyboard compatible
(R)128kb RAM
(E)SIO Port (Atari 8-bit Serial I/O bus)
(X)15 Pin Port (XEGS Keyboard)
(P)POKEY chip (SPU or co-processor)
(Y)Yamaha YM2151 SPU
(H)High Score storage on NVRAM
(U)Upgradeable BIOS. Games marked "U" require a certain Bios version.
Diagnosis software for hardware, cartridges, accessories

Possible software features include:
(L)Extra Level(s)
(M)Extra Music
(S)Extra cut scene(s)

Each hardware and software feature used by the XM should be noted in the tag note.

There's nothing too modern about this expansion module. There are already published games with 128kb RAM, POKEY, and YM2151 chips. The XM expansion prototype was a modified High Score cartridge (a retained feature in the final product). The SIO and 15-pin ports are from before the 7800 (and the 7800 design is derivative of the 5200 and 8-bit designs with said ports). Basically, the XM expansion is a cost effective and convenient amalgamation of existing Atari technology. There's nothing that could be designed for the XM that couldn't be contained in an (overpriced) 7800 cartridge.

The XEGS Keyboard port is made for the XEGS Keyboard. But, developers are already investigating other uses for it.

The Atari SIO port means that games can make use of Single or Double sided standard or High Density 5¼ disk drives, Keyboards, Printers, Tape Drives, Modems, MIDI adapters, RS-232 adapters, Parallel port adapters, Light Pens, Numerical Keypads, Stereo jack, and Additional game controllers Even additional RAM or ROM (up to 256kb, new content for old games, generated content for new games). The port is a serial bus (modern USB actually uses Atari SIO patents), USB file transfer cable, ISA slots adapter (ya, use PC cards on Atari 8-bit), USB peripheral emulator (a PC can emulate any Atari 8-Bit peripheral), and devices can be daisy chained. A prototype 3½ disk drive for Atari 8-bit proves the possibility of using 3½ disks for 7800 games. All of this is pre-7800 technology; so again, there's no modernizing to offend the purists. Additionally, odd homebrew hardware has been made for the SIO port including webcams, IDE and SCSI interface for CD and Hard Dives (you can even boot from this interface), SD drive (also bootable), Wii-Nunchuk port (includes motion), 4 and 8 port controller adapters.

All Atari controllers had adapters to use them in Atari SIO ports; so trak-balls, mice, joysticks, paddles, keypads, touchpads, light guns, or whatever controllers can be added to the 7800's two standard controllers. On 8-bit computers, these adapters were meant to replace functions missing from older systems (Atari 400 had 4 joystick ports, later systems used 2 ports, then 1 port, then none). These systems all mapped 4 joystick ports in the hardware despite missing the connectors. The adapters simply replaced the ports that were missing. But the XM expansion has a bios to sit between the controllers and the game so there is no 4 port hardware limit. Perfect for adding 2 to 8 or even more controllers (I'm sure some homebrewer is working on Gauntlet II).

Additional RAM is intended to store extra graphics pallets (more colors, just not at the same time per sé), additional sprites (more like an NES game), and larger levels. Developers are free to find other uses. Such as more music and sound effects.


Atari 7800 22

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