LCD Controller Registers
11-35
LCD Controller
Horizontal Synchronization Pulse Width (HSW)
The 6-bit horizontal synchronization pulse width (HSW) field is used to specify
the pulse width of the line clock in passive mode or horizontal synchronization
pulse in active mode. LCD.HS is asserted each time a line or row of pixels is
output to the display and a programmable number of pixel clock delays have
elapsed. When line clock is asserted, the value in HSW is transferred to a 6-bit
down counter that uses the programmed pixel clock frequency to decrement.
When the counter reaches zero, the line clock is negated. HSW can be pro-
grammed to generate a line clock pulse width ranging from 1 – 64 pixel clock
periods (program to value required minus one).
Note:
The pixel clock does not transition during the line clock pulse in passive dis-
play mode, but transitions in active display mode. Also, the polarity (active
and inactive state) of the line clock is programmed using the invert HSYNC
(IHS) bit in LCDTiming2.
Pixels-Per-Line (PPL)
The pixels-per-line (PPL) bit-field is used to specify the number of pixels in
each line or row on the screen. PPL is a 10-bit value that represents 16 – 1024
pixels-per-line. PPL is used to count the correct number of pixel clocks that
must occur before the line clock can be pulsed. (The bottom four bits of this
register are not used and always read 1).
Note:
PPL must be programmed to the value required minus one (that is, 0x27F
for a 640 pixels per line LCD panel).