Datasheet

PIC18F85J90 FAMILY
DS39770C-page 186  2010 Microchip Technology Inc.
16.9 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. Writing pixel data at the frame
boundary allows a visually crisp transition of the image.
This interrupt can also be used to synchronize external
events to the LCD. For example, the interface to an
external segment driver can be synchronized for
segment data update to the LCD frame.
A new frame is defined to begin 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 16-17. The LCD controller
will begin to access data for the next frame within the
interval from the interrupt to when the controller begins
to access 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 wave-
forms, and the LMUX<1:0> bits are not equal to ‘00’,
there are some additional issues that must be
addressed. Since the DC voltage on the pixel takes two
frames to maintain zero volts, the pixel data must not
change between subsequent frames. If the pixel data
were 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. There-
fore, when using Type-B waveforms, the user must
synchronize the LCD pixel updates to occur within a
subframe after the frame interrupt.
To correctly sequence writing while in Type-B, the
interrupt will only occur on complete phase intervals. If
the user attempts to write when the write is disabled,
the WERR (LCDCON<5>) bit is set.
FIGURE 16-17: EXAMPLE WAVEFORMS AND INTERRUPT TIMING
IN QUARTER DUTY CYCLE DRIVE
Note: The interrupt is not generated when the
Type-A waveform is selected and when the
Type-B with no multiplex (static) is
selected.
Frame
Boundary
Frame
Boundary
LCD
Interrupt
Occurs
Controller Accesses
Next Frame Data
TFINT
TFWR
TFWR =TFRAME/2 * (LMUX<1:0> + 1) + TCY/2
T
FINT =(TFWR/2 – (2 TCY + 40 ns)) Minimum = 1.5(TFRAME/4) – (2 TCY + 40 ns)
(T
FWR/2 – (1 TCY + 40 ns)) Maximum = 1.5(TFRAME/4) – (1 TCY + 40 ns)
Frame
Boundary
V
3
V
2
V
1
V
0
V
3
V
2
V
1
V
0
V
3
V
2
V
1
V
0
V
3
V
2
V
1
V
0
COM0
COM1
COM2
COM3
2 Frames