TVP3020 datasheet(27/98 Pages) TI

27 / 98 page

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

Direct-Color Mode

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.

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)

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 1280 x 1024 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.

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