
2–32
When VGA is disabled, OVS is sampled on the falling edge of VCLK and then resampled on the rising edge
of RCLK before being passed to the RCLK and dot-clock pipeline delay. When VGA is enabled, then OVS
is sampled on the rising edge of CLK0 and passed to dot-clock pipeline delay. In this way, the video-timing
relationship is maintained since the same method and pipeline delay are applied to the SYSBL and VGABL
signals.
Figure 2–12 demonstrates the use of OVS to produce a custom overscan screen border.
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Overscan Border
OVS
Blank
Display Area
Figure 2–12. Overscan
2.8
Horizontal Zooming
Both the TVP3010C and the TVP3010M palette supports a user-programmable horizontal 2-, 4-, 8-, 16-,
or 32-
x
zooming function. Zooming can be controlled through the auxiliary-control register on the indirect
register map as shown in Table 2–16. Note that the RCLK/SCLK divide ratio also has to be modified in the
output-clock selection register.
Table 2–16. Zoom Control
ACR7
ACR6
ACR5
HORIZONTAL ZOOM
0
0
0
1x
0
0
1
2x
0
1
0
4x
0
1
1
8x
1
0
0
16x
1
0
1
32x
When one of the horizontal-zoom factors (besides 1
×
) is chosen, the internal pixel-data multiplexer is
configured such that it replicates the pixel data on successive dot clocks by the number of times specified
by ACR(5–7). Also, modifying the RCLK/SCLK divide ratio in the output clock selection register facilitates
the pixel replication. The new RCLK divide ratio should be chosen as the old RCLK divide ratio multiplied
by the zoom factor. It is recommended that the zoom only be changed during vertical retrace.