PIC16F913 datasheet(123/272 Pages) MICROCHIP

123 / 272 page

Preliminary

DS41250E-page 121

PIC16F917/916/914/913

9.8

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.

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

(TFINT), as shown in Figure 9-16. 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 (TFWR). New data

must be written within TFWR, 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<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. Therefore, 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 9-16:

WAVEFORMS AND INTERRUPT TIMING IN QUARTER-DUTY CYCLE DRIVE

(EXAMPLE – TYPE-B, NON-STATIC)

Note:

The interrupt is not generated when the

Type-A waveform is selected and when the

Type-B

with

multiplex

(static)

selected.

Frame

Boundary

Frame

Boundary

LCD

Interrupt

Occurs

Controller Accesses

Next Frame Data

TFINT

TFWR

TFWR =TFRAME/2*(LMUX<1:0> + 1) + TCY/2

TFINT =(TFWR/2 – (2 TCY + 40 ns))

→ minimum = 1.5(TFRAME/4) – (2 TCY + 40 ns)

(TFWR/2 – (1 TCY + 40 ns))

→ maximum = 1.5(TFRAME/4) – (1 TCY + 40 ns)

Frame

Boundary

COM0

COM1

COM2

COM3

2 Frames

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