RIVA128 datasheet(56/77 Pages) STMICROELECTRONICS

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128-BIT 3D MULTIMEDIA ACCELERATOR

RIVA 128

56/77

Figure 60.

Interface to monitor or television

Monitor detection

Figure 60 shows the typical connection of a televi-

sion or computer monitor to the RIVA 128s’ DAC

outputs. The RIVA 128 expects only one output

display device to be connected at a time and does

not support simultaneous output to both the moni-

tor and television.

During system initialization, the BIOS detects if a

monitor is connected by sensing the doubly-termi-

nated 75

Ω load (net 37.5Ω). When no monitor is

connected, only the local 75

Ω load is detected and

the RIVA 128 switches to television output mode.

The BIOS sets the CRTC registers to generate the

appropriate timing for the local television standard

and the DACs are adjusted to compensate for the

single 75

Ω load.

Monitor mode is always selected if a monitor is de-

tected since it is assumed to be the output device

of choice, having a higher display fidelity than tele-

vision.

Timing generation

Televisions contain two Phase-Locked Loops

(PLLs). One PLL locks the horizontal frequency

and is used to synchronize horizontal and vertical

flyback, and to keep the active video region stable

and centered. The second PLL locks the color

subcarrier frequency (NTSC 3.5794545MHz or

PAL 4.43361875MHz). The color subcarrier is

used as a phase reference to extract the color in-

formation from the television signal.

The RIVA 128 encodes horizontal and vertical tim-

ing on a composite

sync signal.

Using

13.5000MHz reference clock, the RIVA 128 timing

generator creates ITU-R-601 NTSC and PAL

compliant horizontal timing with only ppm (parts

per million) error. The RIVA 128 does not use the

color subcarrier clock internally. The reference

clock source can be located on the television up-

grade module with the video encoder and TV out-

put connectors, thus lowering the base system

cost.

Flicker filter

RIVA 128 provides an optional flicker filtering fea-

ture for TV and interlaced displays.

Without flicker filtering, elements of an image

present on either the odd or the even field, but not

both, are seen to flicker or shimmer obtrusively.

This is a problem especially with 1-pixel-wide hor-

izontal lines often originating from computer gen-

erated GUI displays.

Flicker filtering causes a slight smearing of pixels

in the vertical direction. This trades off image qual-

ity versus flicker. The displayed pixel contains a

proportion of the data for the pixel on that line, plus

a smaller proportion of the data of the equivalent

pixel on the line above and on the line below.

Overall, the proportions add up to 1 so that the

brightness of the screen does not alter and the pix-

el data does not get clipped.

Flicker filtering only takes place on pixel data from

the framestore - the pattern written into the cursor

already has flicker removed. No flicker removal is

performed on video images.

Overscan and underscan

The RIVA 128 supports overscan and underscan

in the horizontal and vertical directions using hard-

ware scaling. Underscan allows 640x480 resolu-

tion to fit onto NTSC displays and 800x600 resolu-

tion to fit onto PAL displays. Scaling can be adjust-

ed and controlled by software to suit specific TV

requirements. The TV output image position is

also software controllable.

RIVA 128

Monitor

Y/C

TV RGB

Encoder

PAL/NTSC

Television

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