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ATARI XE SYSTEM
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(pictures copyright by M.A.Grundke)

ATARI® ATARI XE SYSTEM ATARI CORPORATION MADE IN TAIWAN ATARI CORPORATION, SUNNYVALE, CA. 94086 SERIAL NUMBER: A18 6 4 032564

Overview of the XE SYSTEM's board: beginning from the right, first interesting thing is the keyboard connector, which is XE SYSTEM-specific (below power-input and peripheral (SIO) port). Below that the two tiny 64Kx4 RAMs (U2,U3). Moving to the board's middle, biggest thing here is the cartridge connector with the ROM (C101687-001, U7) below it, and little MMU (U12) to its right. Further down, beneath a silkscreening (C100417 REV.A XE-SYSTEM) you can see POKEY (U4), CPU (U5) and FREDDIE (U6). Now right from POKEY, still under the ROM and MMU, ANTIC (U8) is to be found, with PIA (U14) to its right (next are the two joystick ports at the board's right side). Finally, below ANTIC and PIA resides GTIA (U15). Other interesting things are the four switches (SW2-SW5) in the board's bottom right (used for the START-, SELECT-, OPTION- and RESET-keys on top of the machine), as well as the power switch (SW1) and power led (LED1) on the left side, directly below the keyboard connector. By the way, like most of ATARI's videogame consoles, the XE SYSTEM's board is completely shielded, on the upper as well as on the lower side. I guess that's because for 'toys' (like videogames), there must be stricter regulations, as far as emissions are concerned

board silkscreening, part 1 (left above cartridge slot): CA200073- (field left blank)

board silkscreening, part 2 (left below cartridge slot): ATARI (R)

board silkscreening, part 3 (below cartridge slot), and POKEY: C100417 REV.A XE-SYSTEM Before it you can see the XE SYSTEM's soundchip, C012294B-01 'POKEY', which was also used in the earlier 400/ 800, the XL-series and some arcade machines. Apart from producing sound, it also provides several other I/O-functions, such as serial I/O (SIO) and controller-input (via its eight potentiometer-inputs). Additionally, it's got 3 timers and a random number generator

The C014806-12 (also called SALLY or 6502C) is a special, ATARI-customized version of the well-known MOS 6502-microprocessor (i.e. 6502B). It has been adopted to work with ANTIC's DMA-mode by adding a HALT signal. Because the 6502C was not yet available, earlier 400/ 800 and XLs used a standard-6502, and as a result required four more special ICs for use with ANTIC. So using the 6502C aka SALLY is another approach to cost-reduction and more reliability

This little one is the XE SYSTEM's MMU, C101686. Its task is to do memory address selection for bus operations. For that purpose, it has several SELECT lines connected to all important parts of the machine's architecture, such as RAM, internal & external ROM and the devices (i.e. the machine's customchips). It is required since the CPU alone couldn't address all these devices directly, because of its limited address space. Note that this chip was used in the whole XL/ XE-series, but with different part numbers (most 1200XL came with a C060609, later XL/XE had a C061618)

C061991-01 'FREDDIE' is a RAM address multiplexer. It is responsible for memory timing and decoding issues, and replaces some logic circuits used on the XL-series' boards (which was done for cost-reduction). In the ATARI 130XE, by the way, it works closely together with C025953 (EMMU), which does the machine's bankswitching and allows, for example, that ANTIC and SALLY can work independantly in one RAM bank each (thus the CPU doesn't need to be HALTed). However, since the XE SYSTEM comes with only 64 KB, there's no need for a C025953 EMMU and for FREDDIE's additional functions

Two pieces NEC D41464C-20 provide the machine's 64 KByte RAM. Using these 64Kx4 RAMs doesn't only reduce the cost in comparison to the older XLs (which used 8 pcs. 64Kx1 and thus additional parts), but also increases reliability, reduces power consumption and, of course, the space required for the RAM bank

C101687-001, the XE SYSTEM's ROM, which is 32 KBytes in size. It is a combination of ATARI XL/XE OS Rev.4, ATARI BASIC Rev.C and the built-in game Missile Command (which is started if you power up the machine without a cartridge and keyboard). Speaking of cartridges, the machine's 30 pin cartridge interface (you can see part of it behind the ROM), is of course fully compatible with all XL/ XE-series cartridges

C021698-01 'ANTIC' controls 'GTIA', which does the TV output. It is a true microprocessor and thus processes programs, the so-called display lists, which contain commands for GTIA. Furthermore, it makes use of a special DMA-transfer mode to fetch data directly from memory, while stopping the CPU with its HALT line (an 'ATARI specific DMA'). ANTIC also provides NMI service to the CPU ('non-maskable interrupt') and displays the characters. Important for games, by the way, is its 'fine scrolling' ability. But the above-mentioned display-lists have even more potential: by combining two display modes, it is possible to display all 256 colors simultaneously (by using one mode for hues, the other for luminances. 16 hues * 16 luminances = 256 colors!). These great capability could often be seen in graphic demos

C014889-01 'GTIA' works closely together with ANTIC. Apart from outputting the graphics (like a CRTC) and various I/O-functions it also provides collision-detection, priority- and player/ missile control (all important mostly for games). It also has I/O-ports to sense joystick-events (e.g. button-press). Early US-XLs came with GTIA's predecessor, CTIA, which lacked some of GTIA's display modes

PIA ('Peripheral Interface Adaptor') is, in XL/XE-design (and similar ones), mainly responsible for controlling joystick I/O (not the joystick triggers, as this is done by CTIA/ GTIA). But also basic peripheral functions (like the SIO-port) and the interrupt lines are controlled by PIA. Note that this one hasn't got an ATARI partno. or label, but that of its original manufacturer, Hitachi HD68B21P. ATARI part numbers for PIA are C014795 or C012298

Also see the CBM 3016 page for MOS 6502-picture, ancestor of the 6502C!

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