Microchip Technology ARD00385 Data Sheet
PIC18F87K90 FAMILY
DS39957D-page 286
2009-2011 Microchip Technology Inc.
20.7
LCD Frame Frequency
The rate at which the COM and SEG outputs change is
called the LCD frame frequency.
called the LCD frame frequency.
TABLE 20-5:
FRAME FREQUENCY
FORMULAS
FORMULAS
TABLE 20-6:
APPROXIMATE FRAME
FREQUENCY (IN Hz) USING
F
FREQUENCY (IN Hz) USING
F
OSC
AT 32 MHz, TIMER1 AT
32.768 kHz OR INTRC OSC
20.8
LCD Waveform Generation
LCD waveform generation is based on the philosophy
that the net AC voltage across the dark pixel should be
maximized and the net AC voltage across the clear
pixel should be minimized. The net DC voltage across
any pixel should be zero.
The COM signal represents the time slice for each
common, while the SEG contains the pixel data.
The pixel signal (COM-SEG) will have no DC
component and can take only one of the two rms values.
The higher rms value will create a dark pixel and a lower
rms value will create a clear pixel.
As the number of commons increases, the delta
between the two rms values decreases. The delta
represents the maximum contrast that the display can
have.
The LCDs can be driven by two types of waveforms:
Type-A and Type-B. In a Type-A waveform, the phase
changes within each common type, whereas a Type-B
waveform’s phase changes on each frame boundary.
Thus, Type-A waveforms maintain 0 V
that the net AC voltage across the dark pixel should be
maximized and the net AC voltage across the clear
pixel should be minimized. The net DC voltage across
any pixel should be zero.
The COM signal represents the time slice for each
common, while the SEG contains the pixel data.
The pixel signal (COM-SEG) will have no DC
component and can take only one of the two rms values.
The higher rms value will create a dark pixel and a lower
rms value will create a clear pixel.
As the number of commons increases, the delta
between the two rms values decreases. The delta
represents the maximum contrast that the display can
have.
The LCDs can be driven by two types of waveforms:
Type-A and Type-B. In a Type-A waveform, the phase
changes within each common type, whereas a Type-B
waveform’s phase changes on each frame boundary.
Thus, Type-A waveforms maintain 0 V
DC
over a single
frame, whereas Type-B waveforms take two frames.
through
provide waveforms
for static, half-multiplex, one-third multiplex and quarter
multiplex drives for Type-A and Type-B waveforms.
multiplex drives for Type-A and Type-B waveforms.
Multiplex
Frame Frequency =
Static
Clock Source/(4 x 1 x (LP<3:0> + 1))
1/2
Clock Source/(2 x 2 x (LP<3:0> + 1))
1/3
Clock Source/(1 x 3 x (LP<3:0> + 1))
1/4
Clock Source/(1 x 4 x (LP<3:0> + 1))
Note:
Clock source is (F
OSC
/4)/8192,
Timer1 Osc/32 or INTRC/32.
LP<3:0>
Static
1/2
1/3
1/4
1
125
125
167
125
2
83
83
111
83
3
62
62
83
62
4
50
50
67
50
5
42
42
56
42
6
36
36
48
36
7
31
31
42
31
Note 1:
If Sleep has to be executed with
LCD
LCD
Sleep enabled (SLPEN
(LCDCON<6>) = 1), care must be taken
to execute Sleep only when V
to execute Sleep only when V
DC
on all
the pixels is ‘0’.
2:
When the LCD clock source is (F
OSC
/4)/
8192, if Sleep is executed irrespective of
the LCDCON<SLPEN> setting, the LCD
goes into Sleep. Thus, take care to see
that V
the LCDCON<SLPEN> setting, the LCD
goes into Sleep. Thus, take care to see
that V
DC
on all pixels is ‘0’ when Sleep is
executed.