Functional Description
1380
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
LCD Controller
LCDCP = System Clock / CLKDIV
where CLKDIV is a field in the LCD Control (LCDCTL) register. The value of CLKDIV should not be 0 or 1
in Raster Mode. The pixel clock operates differently depending on the mode of the LCD controller:
•
Passive (STN) mode: LCDCP only transitions when valid data is available for output. It does not
transition when the horizontal clock (HSYNC) is asserted or during wait state insertion.
•
Active (TFT) mode: LCDCP continuously toggles as long as the Raster Controller is enabled.
20.3.1.2 HSYNC Horizontal Clock (LCDLP Signal)
HSYNC (LCDLP signal) toggles after all pixels in a horizontal line have been transmitted to the LCD and a
programmable number of pixel clock wait states have elapsed both at the beginning and end of each line.
The LCD Raster Timing 0 (LCDRASTRTIM0) register, offset 0x02C, fully defines the behavior of this
signal.
HSYNC can be programmed to be synchronized with the rising or falling edge of the pixel clock (LCDCP).
The PXLCLKCTL and PSYNCRF bits in the LCD Raster Timing 2 (LCDRASTRTIM2) register, offset
0x034, are used to configure the synchronization.
•
Active (TFT) mode: The horizontal clock or the line clock is also used by TFT displays as the horizontal
synchronization signal (HSYNC).
The timings of the horizontal clock (line clock) pins are programmable to support:
–
Delay insertion both at the beginning and end of each line
–
Line clock polarity
–
Line clock pulse width, driven on rising or falling edge of pixel clock
20.3.1.3 VSYNC Vertical Clock (LCDFP Signal)
VSYNC (LCDFP signal) toggles after all lines in a frame have been transmitted to the LCD and a
programmable number of line clock cycles has elapsed both at the beginning and end of each frame. The
LCD Raster Timing 1 (LCDRASTRTIM1) register, offset 0x030, fully defines the behavior of this signal.
VSYNC can be programmed to be synchronized with the rising or falling edge of LCDCP pixel clock. The
PXLCLKCTL and PSYNCRF bits in the LCD Raster Timing 2 (LCDRASTRTIM2) register, offset 0x034,
are used to configure the synchronization.
•
Passive (STN) mode: The vertical, or frame, clock toggles during the first line of the screen.
•
Active (TFT) mode: The vertical, or frame, clock is also used by TFT displays as the vertical
synchronization signal (VSYNC). The timings of the vertical clock pins are programmable to support:
–
Delay insertion both at the beginning and end of each frame
–
Frame clock polarity
20.3.1.4 LCD AC Bias Enable (LCDAC)
•
Passive (STN) mode: To prevent a DC charge within the screen pixels, the power and ground supplies
of the display are periodically switched. The Raster Controller signals the LCD to switch the polarity by
toggling this pin.
•
Active (TFT) mode: This signal acts as an output enable (OE) signal. It is used to signal the external
LCD that the data is valid on the data bus.
20.3.2 LCD DMA Engine
The LCD DMA engine can output graphics data to constantly refresh the external LCD display, without
burdening the CPU, through interrupts or a firmware timer. The DMA operates on one or two frame
buffers, which are set up during initialization. Using two frame buffers (ping-pong buffers) enables the
simultaneous operation of outputting the current video frame to the external display and updating the next
video frame. The ping-pong buffering approach is preferred in most applications.