VGA32_16BPP Controller - Color output using the NanoBoard-NB1

The R, G and B outputs from the VGA32_16BPP Controller are 5, 6 and 5 bits in length respectively. Together, these outputs form the 16-bit RGB value required for driving the red, green and blue color guns of the target monitor.

On Altium's Desktop NanoBoard NB2DSK01 (with attached Audio/Video peripheral board PB01), or a custom/production board, you can take full advantage of this support and the subsequent range of 65536 colors that can be achieved. When using the NanoBoard-NB1 however, on-board 2-bit digital to analog converter circuitry (Figure 1) provides a limitation to the number of colors that can be used/achieved

Figure 1. Digital to Analog RGB conversion.

The R, G and B outputs must, in the case of using the NanoBoard-NB1, be reduced to 2-bit signals through the use of relevant bus joiners, as illustrated in Figure 2. The most significant 2 bits are used in each case.

Figure 2. Color output bit reduction.

For each color, the 2-bit digital signal can be converted into 4 distinct analog levels. These levels specify the intensity of each of the three primary colors to use when displaying the pixel on the monitor's screen. The levels range from 0V (total darkness) to 0.7V (maximum brightness).

With each analog input being one of four possible levels, the monitor can display each pixel on the screen with one of 64 different color permutations.