Standard Television Interface Circuit
The AY-3-8900, also known as the Standard Television Interface Chip or STIC, is a video display controller (VDC) produced by General Instrument for use with their CP1600 CPU in games consoles.[1] It is best known as the basis for the Mattel Intellivision.[2][1][3][4]
The STIC is typical of VDCs of the era, using a grid of character-like cells to draw a background graphic and then using up to eight sprites they called "movable objects" (MOBs), to produce animation. The overall resolution is 167 × 105 pixels in NTSC (in the 8900-1 model) and 168 × 104 pixels in PAL (8900 model),[1] but only visible in an area of 159 × 96 pixels. The extra pixels around the visible area allow sprites to be placed in those locations and then smoothly move on-screen. The background consists of a 20 × 12 grid of 8×8 patterns known as "cards", which can be used as characters or other shapes. The STIC also computes collision information between the objects and screen borders.
Characteristics
[edit]- able to operate up to 4 MHz, but is generally run at 3.579545 MHz (NTSC)
- 14-bit multiplexed data/address bus shared with CPU
- 20×12 tiled playfield, tiles are 8×8 pixels for a resolution of 159×96 (right pixel not displayed)
- 16 color palette, two colors per tile
- Foreground/Background mode; all 16 colors available for background and colors 1–8 available for foreground per tile; grom cards limited to the first 64
- Color Stack mode; all 16 colors available for foreground per tile; background colour from a four colour rotating stack of any four colors, all 277 grom and gram cards available
- Colored Squares mode[5] allows each tile to have four different colored 4×4 blocks as in Snafu); first seven colors available for foreground blocks; background colour from the color stack
- 8 sprites (all visible on the same scanline). Hardware supports the following features per-sprite:
- coordinate addressable off screen for smooth edge entries and exits
- Size selection: 8×16 or 8 pixels wide by 8 half-pixels high
- Stretching: horizontal (1× or 2×) and vertical (1×, 2×, 4× or 8×)
- Mirroring: horizontal and vertical
- Collision detection: sprite to sprite, sprite to background, and sprite to screen border
- Priority: selects whether sprite appears in front of or behind background.
- fine horizontal and vertical pixel scrolling
- all STIC attributes and GRAM re-programmable at VBLANK, 60 times a second
Color Palette
[edit]The chip generates a sixteen color palette, based on four bit input and divided into two sets. The following table shows bit and YIQ values as presented in technical information:[3][6][7]
| Color Set | Color | Bits | Y | I | Q |
|---|---|---|---|---|---|
| Primary | Black | 0000 | 0.000 | 0.000 | 0.000 |
| Blue | 0001 | 0.330 | -0.733 | +0.660 | |
| Red | 0010 | 0.523 | +0.666 | +0.200 | |
| Tan | 0011 | 0.715 | +0.266 | -0.133 | |
| Dark Green | 0100 | 0.413 | -0.133 | -0.600 | |
| Green | 0101 | 0.577 | -0.200 | -0.533 | |
| Yellow | 0110 | 0.853 | +0.533 | -0.333 | |
| White | 0111 | 1.000 | 0.000 | 0.000 | |
| Pastel | Gray | 1000 | 0.550 | 0.000 | 0.000 |
| Cyan | 1001 | 0.660 | -0.533 | -0.266 | |
| Orange | 1010 | 0.687 | +0.533 | -0.066 | |
| Brown | 1011 | 0.330 | +0.266 | -0.266 | |
| Magenta | 1100 | 0.550 | +0.400 | +0.667 | |
| Light Blue | 1101 | 0.660 | -0.400 | +0.400 | |
| Yellow-Green | 1110 | 0.687 | +0.066 | -0.533 | |
| Purple | 1111 | 0.440 | +0.133 | +0.533 |
Note: The displayed colors are approximate. Actual tones varied according to the analog television standard and quality of the CRT display.
See also
[edit]References
[edit]- 1 2 3 "9. Video". Microelectronics Data Catalog (PDF). General Instrument Corporation. 1982. pp. 9–43, 9–44, 9–45.
- ↑ Harley, David (2006). "Mattel Intellivision FAQ". www.intellivision.us.
- 1 2 Zbiciak, Joe. "STANDARD TELEVISION INTERFACE CIRCUIT (STIC)". jzIntv!. Retrieved 2019-07-23.
- ↑ "STIC – Intellivision Wiki". wiki.intellivision.us.
- ↑ "Intellivision Classic Video Game System / Intellivision Master Component". Intellivision Lives. Archived from the original on 2017-06-30.
- ↑ Requirements of a PAL color circuit for the Mattel Electronics Intellivision Master Component (PDF). Mattel Toys. January 17, 1980.
- ↑ Woods; Palazzolo (June 29, 2022). "General Instruments AY-3-8900-1 a.k.a. Standard Television Interface Chip (STIC) emulation for Mattel Intellivision". GitHub.