Television Interface Adaptor
Mayer and Milner arranged to speak to the chip's designer, Chuck Peddle, on using the 6502 as the basis for their programmable video game console.
[8] Using a breadboard prototype for the display adapter atop a 6502 testbed system, Milner was able to demonstrate the ability to program a simple version of their Tank game.
Joe Decuir was hired on to help convert Milner's proof-of-concept to a functional prototype, sufficient for Atari to give the go-ahead for the development to continue.
[4] While Decuir worked on the design of the rest of the system, Jay Miner focused on making an ASIC for the display adapter.
[10] To start the process, the game program running on the MOS Technology 6502-based CPU loads the TIA's registers with the data needed to draw the first line of the display.
Generally the analog side of the display system generates an interrupt when it finishes drawing a raster line and is getting ready for the next one.
[4] This suspends the operation of the CPU until the start (color clock cycle 0) of the horizontal blanking period right ahead of the next line, providing a measure of automatic synchronization.
[4] In addition, the TIA only semi-automatically generates vertical sync timing signals (to mark the end of each video frame and the start of the next).
Like for the RDY-wait hardware, the vertical sync signal is triggered by the CPU writing to a specific TIA register address.
If no write to that address was ever done and the TIA was allowed to free-run, it would generate a single infinite frame of active raster lines, which would typically appear on the TV as a rolling picture.
[11] Given this complexity, early games using the system tended to be simple in layout, using the TIA to create symmetric playfields with players on top.
A key advance was the licensing of Space Invaders for the platform, which required many more player graphics to draw the enemy aliens.
Adventure uses this concept to produce a wide variety of maps by combining different portions of the data in ROM, jumping back and forth through it during the screen drawing.
As programmers grew more accustomed to the odd timing needed to get things to work properly on-screen, they began to use the inherent flexibility in the TIA to greatly improve the displays.
One common technique was to change the color registers that were used to draw the 1 and 0 states of the playfield, resulting in displays with rainbow-like effects.
The TIA is capable of generating different types of pulse waves and white noise output to its two oscillators (or channels) AUD0 and AUD1.
