Atari 65xe Motherboard
The Atari 65xe motherboard system is an 8-bit personal computer made up of several component parts that compliment the entire assembly.
It is contained inside a plastic case that protects the internal motherboard. The newer assembly design was a far cry from the original series that was surrounded by a cast aluminum block. It is powered by a 6502 processor chip designed by Chuck Peddle and a team at MOS Technology in 1971.
The Atari Chipsets and History
The history of Atari’s chipsets began with the Atari 2600 console that was developed in the early 70’s. At that time Atari implemented a chip known as the TIA (Television Interface Adapter) that represents “players” and “missiles” as distinct moving objects. It used a 20-bit memory register that to emulate a 40-bit display on the right side of the screen. It had the ability to show from 1-4 colors contained in a palette of 128 various colors. The players and missiles had the ability to travel horizontal across the screen. Learn more on the Atari Player Missile Graphics page.
CTIA Chip (earlier revision of TIA)
Much later a newer chip was needed as an upgrade for the Atari 65xe Motherboard. It modeled after the TIA design having twice the resolution being able to display double the number of colors. This allowed a higher resolution expanding to 320 across the screen. Other advancements were made with this new chip known as the CTIA adding four 8-bit players, four 2-bit missiles, with the ability to merge all 4 missles into a 5th player.
As the Atari computer began to gain notoriety for some much needed improvements for their graphics, work began on housing a new chip for the Atari 65xe Motherboard to support CITA known as GTIA. Many new modifications were made to allow vertical movement as well. This also included creating missiles the height of the display screen and providing separate color registers for them. Also something called “color merging” created newer colors when an overlap occurred. Collision detection was also enabled for the players, missiles, and the playfield graphics.
For the high resolution display, this new chip provided the ability to obtain 16 colors extracted from a single hue. Several Graphics modes were developed such as Graphics 9, Graphics, 10, and Graphics 11, each occupying their own color ranges and display screen coordinates (for the width and height).
Interestingly also is that the GITA chip utilizes three pins to obtain a read from the console keys, Start, Selection, and Option. Also section processes the function keys, manages the keyboard beep, and monitors controller trigger lines.
Atari introduced the POKEY (Pot Keyboard Integrated Circuit) for their arcade games in the early 80’s. It includes function sampling for game paddles, scanning of keyboard switches, and provides sound output. The POKEY chip provides 4 voices, each with their own square wave sound, with can also have various other distortion ranges. Audio timer interrupts can also be created to set interrupts. Also the ability to generate a random number is found here, plus reading of the serial I/O port, and up to eight IRQ interrupts.
In later models, Atari introduced the FREDDIE chip, which contained 40 pins. It was used to replace other expensive chips to include a RAM address multiplexer for DRAM accessibility. With this chip, the system can reference memory locations independent from the CPU and ANTIC.
The register flags, interconnections, arithmetic logic, control logic, and its operation codes are managed by this chip. The decimal and binary, clock timer, stack pointer, interrupts levels, opcodes, indexing, non maskable input NMI, set overflow, data bus, address bus, and so on are performed by the chip’s circuitry.
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