STG3000X-RIVA128 STMicroelectronics, STG3000X-RIVA128 Datasheet - Page 56

• Manufacturer Part Number: STG3000X-RIVA128
• Description: 128-BIT 3D MULTIMEDIA ACCELERATOR
• Manufacturer: STMicroelectronics

RIVA 128
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
connected, only the local 75 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
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 a
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
56/77
load.
load (net 37.5 ). When no monitor is
RIVA 128
TV RGB
Encoder
R
G
B
75 75 75
R
G
B
Y/C
Y
C
75
75
75
128-BIT 3D MULTIMEDIA ACCELERATOR
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.
PAL/NTSC
Television
75
75
75
Monitor