![](http://datasheet.mmic.net.cn/390000/TVP3020-175_datasheet_16839163/TVP3020-175_27.png)
2–13
Submode 4 uses eight bit planes to address the color palette. Since all eight bits of palette address are
specified from the pixel port, the page register is not used. This mode allows dot clock-to-LCLK ratios of 1:1
(8-bit bus), 2:1 (16-bit bus), 4:1 (32-bit bus) or 8:1 (64-bit bus). Therefore, in a 64-bit configuration, a 1024
by 768 pixel screen can be implemented with an external data rate of only 8 MHz.
NOTE:
If externally clocked-frame buffer timing is used (ACR3 = logic 0, see
Section 2.3.2), only multiplex ratios of 1:1 can be used. See Table 2–6.
The auxiliary window, port select, and color-key switching functions must be
disabled and set for palette graphics when in the pseudo-color mode. This is the
default condition at RESET. See Section 2.6
2.4.4
In direct-color mode, 24, 16, 15, or 12 bits of data can be transferred directly to the RGB DACs but with the
same amount of pipeline delay as the overlay data and the control signals (blank and SYNCs). Depending
on which direct-color mode is selected, overlay is provided by utilizing the remaining bits of the pixel bus
to address the palette RAM. This results in a 24-bit RAM output that is then used as overlay information to
the DACs. The overlay capability is designed to work with the auxiliary window, port select, and color-key
switching functions to provide overlay in specific windows or on a pixel-by-pixel basis on the direct-color
display as discussed in Section 2.6. See Tables 2–6, 2–8, and 2–9 for more details on selecting the
direct-color modes.
Direct-Color Mode
The default condition after reset is for the auxiliary window and port select functions to be disabled
(ACR1 = ACR2 = logic 0). The color-key comparisons, which are controlled by the color-key control (CKC)
register bits 0–3, are also disabled (CKC0 = CKC1 = CKC2 = CKC3 = logic 0). Also, since multiplex-control
register 2 bit 7 = logic 1 and ACR0 = CKC4 = logic 1 at RESET, the default is for VGA pass through. This
is because multiplex-control register 2 bit 7 enables the VGA port and the switching functions
(SWITCH = COLOR-KEY = 1, see Section 2.6) are disabled and set for palette graphics (as opposed to
direct color-palette bypass).
Submode 1 is the 24-bit direct-color mode that uses eight bits to represent each color and eight bits for
overlay. The 64-bit-wide pixel bus of the Viewpoint palette allows multiplex ratios of 1:1 or 2:1. In this mode,
there are basically two different configurations: either the 32-bit data is grouped as overlay, red, green, blue,
or blue, green, red, overlay.
Submode 2 is the XGA-compatible (5–6–5) 16-bit-color mode supporting five bits of red, six bits of green,
and five bits of blue data. Viewpoint supports multiplex ratios for this mode of 1:1, 2:1, and 4:1. With 4:1
multiplexing, the TVP3020 can display 1280x1024 direct-color using 45-MHz VRAM without any glue logic.
Overlay is not available in this mode.
Submode 3 is the TARGA-compatible (5–5–5) mode that uses 15 bits for color and 1 bit for overlay. It allows
5 bits for each of red, green, and blue data. The TVP3020 supports 1:1, 2:1, and 4:1 multiplexing ratios in
this mode.
Submode 4 is (6–6–4) configuration. It provides six bits of red, six bits of green, and four bits of blue. The
TVP3020 also supports 1:1, 2:1, and 4:1 multiplexing in this mode. Overlay is not available in this mode.
Submode 5 is (4–4–4–4) configuration. It provides 12 bits of direct color and 4 bits of overlay. It allows four
bits for each of red, green, and blue data. The TVP3020 supports 1:1, 2:1, and 4:1 multiplexing ratios in this
mode.
See NOTES in the following section.