LCD Controller Registers
11-38
Figure 11–16.
Passive Mode End of Frame Timing
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ
VFP=1
LCD.VS
LCD.P
LCD.HS
VSW=1
VBP=2
First
line of
frame
n+1
Second
line of
frame
n+1
Third
line of
frame
n+1
Last
line of
frame
n
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 to add extra
dummy horizontal synchronization delays (i.e., dummy lines or rows) between
the vertical front porch and vertical back porch in passive mode.
In active mode (LCDTFT = 1), LCD.VS is used to generate the vertical syn-
chronization signal. It is asserted each time the last line or row of pixels for a
frame is output to the display and a programmable number of line clock delays
have elapsed. When LCD.VS 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, LCD.VS 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 one).
In passive mode (LCDTFT = 0), VSW does not affect the timing of the LCD.VS
pin, but instead can be used to add extra horizontal synchronization delays
(that is, dummy lines or rows) between the end and beginning of frame line
clock delay counts. The total number of horizontal synchronization delays 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 horizontal synchronization delays
between frames by first using the value in VFP, then VSW, then VBP. In passive
mode, it is irrelevant if one or all three of the fields are used to insert delays;
the user need only ensure that the sum of the values in the three fields is equal
to the total number of line clock delays that are needed between frames.