dsPIC33/PIC24 Family Reference Manual
DS30009740B-page 36 2010-2013 Microchip Technology Inc.
11.0 LCD INTERRUPTS
The LCD timing generation provides an interrupt that defines the LCD frame timing. This interrupt
can be used to coordinate the writing of the pixel data with the start of a new frame, which
produces a visually crisp transition of the image.
This interrupt can also be used to synchronize external events to the LCD. For example, the inter-
face to an external segment driver can be synchronized for segment data updates to the LCD
frame.
A new frame is defined as beginning at the leading edge of the COM0 common signal. The
interrupt will be set immediately after the LCD controller completes accessing all pixel data
required for a frame. This will occur at a fixed interval before the frame boundary (T
FINT), as
shown in Figure 11-1.
The LCD controller will begin to access data for the next frame, within the interval from the inter-
rupt to when the controller begins accessing data after the interrupt (T
FWR). New data must be
written within T
FWR, as this is when the LCD controller will begin to access the data for the next
frame.
When the LCD driver is running with Type-B waveforms and the LMUX<2:0> bits are not equal
to ‘00’, there are some additional issues.
Since the DC voltage on the pixel takes two frames to maintain 0V, the pixel data must not
change between subsequent frames. If the pixel data was allowed to change, the waveform for
the odd frames would not necessarily be the complement of the waveform generated in the even
frames, and a DC component would be introduced into the panel. Because of this, using Type-B
waveforms requires synchronizing the LCD pixel updates to occur within a subframe after the
frame interrupt.
To correctly sequence writing in Type-B, the interrupt only occurs on complete phase intervals. If
the user attempts to write when the write is disabled, the WERR bit (LCDCON<5>) is set.
Note: The interrupt is not generated when the Type-A waveform is selected and when the
Type-B with no Multiplex (Static) is selected.
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