SLAU723A October 2017 – October 2018 MSP432E401Y , MSP432E411Y
A feature exists in the LCD to cover either the top or lower portion of the display with a default color. This feature is called a subpicture and is illustrated in Figure 20-14. Subpictures are only allowed for Active Matrix Mode (when LCDTFT = 0x1 in the LCD Raster Control (LCDRASTRCTL) register).
Subpicture reduce the bandwidth since lines containing default pixel data are not read from memory. For example, suppose the panel has 100 lines of which 50 are default pixel data lines. Then, only 50 lines of data are written by the DMA from DDR for this subpicture setup. That is, the LCD DMA Frame Buffer n Base Address (LCDDMABAFBn) and LCD DMA Frame Buffer n Base Address (LCDDMABAFBn) registers only encompass 50 lines of data instead of 100.
The subpicture feature is enabled when the SPEN control bit in the LCD Raster Subpanel Display n (LCDRASTRSUBPn) register is set to 1. The HOLS bit, when programmed to 0, puts the Default Pixel Data lines at the top of the screen and the active video lines at the bottom of the screen. When the HOLS bit is set to 1, Active video lines are at the top of the screen and Default Pixel Data lines are at the bottom of the screen. The HOLS bit behavior is shown in Figure 20-15.
The LPPT (lines per panel threshold) bit field defines the number of lines at the bottom of the picture for both HOLS = 1 or 0. LPPT is an encoded value in the range [0:2047] used to represent the number of lines in the range [1:2048].