PPL = 3
HSW = 6
HFP = 1
Pixel Clock
(LCD_PCLK)
HBP = 1
LCD_HSYNC
IHS = 0
Last Line of the
Frame is Output to
the Display
Dummy Line Clock
First Line of the
New Frame is Output
to the Display
IVS = 0
VSW = 2
VFP = 1
LPP
VBP = 1
LPP
LCD_VSYNC
Registers
1067
SPRUH82C – April 2013 – Revised September 2016
Copyright © 2013–2016, Texas Instruments Incorporated
Liquid Crystal Display Controller (LCDC)
23.3.10.2
Vertical Synchronization Pulse Width (VSW)
The 6-bit vertical synchronization pulse width (VSW) field is used to specify the pulse width of the vertical
synchronization pulse in active mode or is used to add extra dummy line clock cycles between the vertical
front porch and vertical back porch in passive mode.
23.3.10.2.1 Active Mode
NOTE:
Remember that most of the parameters (HSW, HFP, PPL, HBP) must be programmed to
value required minus 1.
In active mode (TFT_STN = 1), VSYNC is asserted each time the last line or row of pixels from the
previous frame is output to the display and a programmable number of line clock delays (VFP) has
elapsed. When the frame clock (LCD_VSYNC) is asserted, the value in VSW is transferred to a 6-bit down
counter that uses the line clock frequency to decrement. When the counter reaches zero, the frame clock
(LCD_VSYNC) is negated. VSW can be programmed to generate a vertical synchronization pulse width
ranging from 1–64 line clock periods (program to value required minus 1—see
). The
following frame starts after LCD_VSYNC is deasserted and a programmable number of line clock delays
(VBP) has elapsed.
Figure 23-32. Vertical Synchronization Pulse Width (VSW) - Active Mode
23.3.10.2.2 Passive Mode
NOTE:
The pixel clock does not transition during the whole dummy line clock periods that are
inserted in passive mode before the frame pulse. The line clock does transition during the
insertion of the dummy line clock cycles. VSW must be long enough to load the palette.
In passive mode (TFT_STN = 0), VSW does not affect the timing of the frame clock, but instead can be
used to add extra line clock cycles between the end and beginning of frame line clock cycle counts. The
total number of line clock cycles that are inserted between each frame is equal to the sum of the values in
VFP, VSW and VBP. A counter is used to insert dummy line clock cycles between frames by first using
the value in VFP, then VSW, then VBP. You must ensure that the sum of the values in the three fields is
equal to the total number of line clock cycles that are needed between frames. The LCD controller frame
clock pin is asserted on the rising-edge of the first pixel clock for each frame. The frame clock remains
asserted for the remainder of the first line as pixels are output to the display, also during the assertion of
the first line clock for the frame, and then negated on the rising-edge of the first pixel clock of the second
line of each frame.