Back to Table of Contents 4.2 HARDWARE OVERVIEW The Atari 5200 is essentially a console version of the Atari 8-bit Computers (400/800, XL, XE, XEGS). The functions of the system are divided up between four major IC chips: CPU: The CPU in the 5200 is a modified 6502 processor. The only difference is that Atari's version of this CPU has some extra hardware on board that allows the ANTIC chip to take over the bus to do Direct Memory Access (DMA). POKEY: POKEY's main job is to generate sound and to perform a variety of other miscellaneous functions. The POKEY chip has four separate channels, and the pitch, volume and distortion values of each of these channels can be controlled individually. POKEY is also used to read the position of each of the joysticks, and scans the keypad on each controller for key presses. Its other functions include the random number generator, IRQ handling, and 3 high-speed counters. POKEY also has a serial communications port that is connected to the 5200's expansion port. ANTIC: ANTIC can be thought of as the 5200's graphics co-processor. ANTIC has direct access to RAM where it reads a special program called the display list. The display list tells ANTIC exactly how to draw the display and then sends information to the GTIA which generates the actual video signals. The 5200 supports 17 seperate video modes; some are character modes, others graphic. Each mode has a different combination of vertical size, horizontal size, and number of colors. Using the display list, these modes can be mixed freely on a single screen, so for example a screen could have a couple lines of text mode at the top, a block of hi-res graphics in the middle, and more text at the bottom. The location in memory that the display date comes from can easily be controlled through ANTIC. The display data can be almost anywhere in memory, and it is even possible for the data for each line to come from totally different places in memory. This allows horizontal and vertical scrolling to be implemented very easily. ANTIC is also responsible for controlling Non-Maskable Interrupt to the processor. GTIA: The GTIA's main responsibility is to generate the video signals to the TV and to handle sprites. The GTIA is where the actual colors are put into the video signal. The 5200 has a palette of 256 colors. Most video modes only allow four colors, but a facility in the ANTIC chip allows the values of these colors to be changed on each line of the screen, so it is possible to have all 256 colors on screen at once. The 5200 has four player and four missile sprites. Player sprite are eight pixels wide and either 128 or 256 pixels high, missiles are two pixels wide and either 128 or 256 pixels high. Each sprite can have its on color, independent from the normal screen colors. The GTIA chip can detect collisions between players, missiles, and the playfield. This chip is also responsible for reading joystick trigger buttons, and controlling which controller is being read by POKEY. Back to Table of Contents