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With the improvement of information technology, people are increasingly demanding visual appreciation. "Visual impact" has become a standard for people to judge display performance. Visual impact not only requires a large screen size, but also requires the display to be clear, including pictures and text. In order to satisfy this demand, this article takes Jingmei Yage CME-M5 (Jinshan) as an example to analyze how to superimpose characters in HDMI high-definition signals and finally realize the process of high-definition output.
As shown in the figure below, it is not difficult to see that the HDMI high-definition signal is sent to the CME-M5 through the HDMI to RGB chip, and then superimposed with the external character chip, and then sent out through RGB to HDMI.
Aside from other functions, starting from the simplest By-Pass, that is, 150MHz 24bit RGB, without any processing, directly send 150MHz 24 bit RGB, if By-Pass is uncertain, other functions are debugged It is also a loss. The key codes of By-Pass are as follows:
The verification of the gray scale is the easiest to see. Simply add, what is grayscale?
The gray scale represents the level of gradation from the darkest to the brightest. The more intermediate levels, the more delicate the picture will be. Taking the 8-bit panel as an example, it can represent the 8th power of 2, which is equal to 256 brightness levels. We call it 256 gray levels.
Corresponding to the digital logic, the process of R/G/B grading from 0 to 255 is divided into 256 equal parts, incremented to 1, called 256 gray scale; divided into 8 equal parts, the increment value is 32, called 8 gray scale.
The fake design is a 256-level black and white gray screen. The RGB three colors are changed from FF to 00 at the same time, that is, 24 data lines are simultaneously level-flip. This requires the highest power and speed requirements for the FPGA chip, so the special test verification shows that Gray scale can basically verify whether the quality of video transmission is stable and reliable, and other images that are mixed with pictures are actually countless.
Well, let's verify with 256 grayscale as a reference legend.
According to the design of the general CPLD EPM240, the straight-through effect is perfect, no doubt, and has been widely used. The normal effect is as follows, no bright lines, no noise.
The display effect through the M5-ByPass is as follows (a few sample pictures), and the gray lines of several colors appear bright lines.
According to the above, the way of By-Pass like CPLD does not work. Cause grayscale bright line problems, there are generally two:
(1) One is insufficient drive current;
(2) The other is IO or the clock speed can't keep up, the data is not aligned;
Start with the first solution, the default HS, VS output 4mA (default) is changed to 8mA under primace7.2, and the PCLK with faster flip speed is changed to 16mA. However, all the pull-ups are pulled up. After the change, only the yellow gray scale is improved (the bright line is not seen), and the others are not changed.
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