LCD Controller Registers
11-33
LCD Controller
Horizontal Back Porch (HBP)
The 8-bit horizontal back porch (HBP) field is used to specify the number of
dummy pixel clocks to insert at the beginning of each line or row of pixels. After
the line clock for the previous line has been negated, the value in HBP is used
to count the number of pixel clocks to wait before starting to output the first set
of pixels in the next line. HBP generates a wait period ranging from 1 – 256 pixel
clock cycles (program to value required minus one).
Note:
The pixel clock pin LCD.PCLK, does not transition during these dummy pixel
clock cycles in passive display mode (pixel clock transitions continuously in
active display mode).
Figure 11–13 and Figure 11–14 show the use of LCD timing register 0 control
fields for active and passive displays, respectively. Timing is shown for the
middle of a frame, not at the beginning or end where VSYNC also occurs. See
Section 11.8.3, LCD Timing 1 Register, for information on VSYNC timing. In
Figure 11–14, the dashed lines on LCD.PCLK indicate that the signal is not
actively toggling: LCD.PCLK is inactive at end-of-line mode. Virtual clocks are
shown to demonstrate the behavior of the HFP, HSW, and HBP bit fields in the
timing 0 register.
Horizontal Front Porch (HFP)
The 8-bit horizontal front porch (HFP) field is used to specify the number of
dummy pixel clocks to insert at the end of each line or row of pixels before puls-
ing the line clock pin. Once a complete line of pixels is transmitted to the LCD
driver, the value in HFP is used to count the number of pixel clocks to wait be-
fore pulsing the line clock. HFP generates a wait period ranging from 1 – 256
pixel clock cycles (program to value required minus one).
Note:
The pixel clock pin LCD.PCLK, does not transition during these dummy pixel
clock cycles in passive display mode (pixel clock transitions continuously in
active display mode).