Other Parts Discussed in Thread: ALP
I have a DS90UH947 connected to a DS90UH948 which is connected to an LCD via LVDS. The LCD is DE only so no hsynch or vsynch. I'm trying to use the pattern generator in Analog LaunchPAD with internal timing to show color bars on the LCD. My LCD is 1920 x 1080 24-bit color. The pixel clock is 70.93 nominal which is my first problem. According to app note SNLAG132G, the pixel clock is set by a divider using M and N and the internal 200 MHz clock. When I leave M at 1 and change N, the calculated pixel clock values make sense. For example, setting N = 3 would be 200 MHz * (1/3) = 66.7 MHz which is the value in the GUI. But anytime I change the M value, the calculated value is wrong. For example, setting M to 2 and N to 6 should be 200 MHz * (2/6) = 66.7 MHz, but the GUI shows 266.7 MHz. Also the default M/N values of 1/2 show "Invalid" in the GUI. After playing around with the M/N values, the closest I can get to 70.93 MHz is with M/N set to 2/23. That should be 200 MHz * (2/23) = 17.4 MHz, but the GUI shows 69.6 MHz.
My second problem is setting the Synch Width values. My LCD datasheet shows that the horizontal blanking interval is 105 pixel clocks, and the vertical blanking interval is 30 lines. If I set the M/N to 2/23, the hsynch to 105, and the vsynch to 30, I get an error message stating that the "Sum of Active Lines....must be less than Total Lines."
Based on these results, I don't trust the GUI calculation of the pixel clock when M is anything other than 1. So I set M/N to 1/3 which is 66.7 MHz. That's still in the LCD range of 60 to 75 MHz. Then I set the hsynch to 105 and vsynch to 30. The "Status" area shows a frame rate of 26.9 when it should be 60 Hz. And when I enable it nothing happens. In fact the only way I can get anything to show up on the screen is with M/N set to 1/2, hsynch set to 44, and vsynch set to 5. With those values I see color bars on the top half or so of the LCD but with lots of blinking and crossover between the colors.
