TLC34077 Datasheet, PDF (17/41 Pages) Texas Instruments – Video Interface Palette Data Manual

2.4.1 VGA Pass-Through Mode
Mode 0, the VGA pass-through mode, is used to emulate the VGA modes of most personal computers. The
advantage of this mode is that the TLC34077 can take data presented on the feature connectors of most
VGA-compatible PC systems into the device on a separate bus, thus requiring no external multiplexing. This
feature is particularly useful for systems in which the existing graphics circuitry is on the motherboard. In
this instance, it enables implementation of a drop-in graphics card that maintains compatibility with all
existing software by using the on-board VGA circuitry but routing the emerging bit-plane data through the
TLC34077. This is the default mode at power up. When the VGA pass-through mode is selected after the
device is powered up, the clock selection register, the general control register, and the pixel read mask
register are set to their default states automatically.
Since this mode is designed with the feature connector philosophy, all the timing is referenced to CLK0,
which is used by default for VGA pass-through mode. For all the other modes, CLK <0:1> are the oscillator
sources for DOTCLK, VCLK, and LCLK.
2.4.2 Multiplexing Modes
In addition to the VGA pass-through mode, there are three other modes available. Modes 1 and 2 use 8 bit
planes to address the color palette. These modes allow dot-clock-to-LCLK ratios of 1:1 (8-bit bus), or 2:1
(16-bit bus).
2.4.3 True-Color Modes
Mode 3 is the true-color mode in which 24, 16, or 15 bits of data are transferred from the pixel port directly
to the DACs, but with the same amount of pipeline delay as the control signals (BLANK and SYNCs). For
proper true color operation, all overlay bits defined for a given mode should be set to logic ‘0’ or the read
mask must be set to 00h.
Mode 3a is the TARGA compatible (5-5-5) true-color mode. In this 16-bit mode, there are 5 bits of RED, 5
bits of GREEN, 5 bits of BLUE. Refer to Table 2–7 for the exact bit definitions.
Mode 3b is the XGA compatible (5-6-5) true-color mode. This 16-bit mode has 5 bits of RED, 6 bits of
GREEN, and 5 bits of BLUE data. Refer to Table 2–7 for the exact bit definitions.
Mode 3c is a multiplexed version of mode 3a, that allows two 16-bit TARGA-compatible words to be latched
into the TLC34077 pixel port with one LCLK. In this mode, the 16-bit word latched on pixel port inputs
P0–P15 is executed first, while the word latched on P16–P31 is executed last. The user should program
the LCLK divide ratio in the output-clock selection register to /2. Refer to Table 2–7 for the exact bit
definitions.
Mode 3d is a multiplexed version of mode 3b, that allows two 16-bit XGA-compatible words to be latched
into the TLC34077 pixel port with one LCLK. In this mode, the 16-bit word latched on pixel port inputs
P0–P15 is executed first, while the word latched on P16–P31 is executed last. The user should program
the LCLK divide ratio in the output-clock selection register to /2. Refer to Table 2–7 for the exact bit
definitions.
Mode 3e is a 24-bit true-color mode that features 8 bits of data for each color. The order in which the color
fields appear in the 32-bit word are the reverse of mode 3f. Refer to Table 2–7 for the exact bit definitions.
Mode 3f is the 24-bit true-color mode used on the TLC34077. It also features 8 bits of data for each color.
Refer to Table 2–7 for the exact bit definitions.
Since only 5 bits (6 bits for GREEN in Mode 3b and 3d) are provided for each color in the 16-bit true-color
modes (3a – 3d), the color data will be internally shifted by the TLC34077 to the 5 MSB positions (6 MSB
positions for GREEN in Mode 3b and 3d) before being presented to the three color DACs. The remaining
lower 3 bits (Iower 2 bits for GREEN in Modes 3b and 3d) are then set to logic 0.
When in true-color modes 3e or 3f, the data input only works in the 8-bit mode. In other words, if only 6 bits
are to be used, the 2 LSB inputs for each color must be tied to GND. However, the palette, which is used
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