PIC16F1938 Datasheet, PDF (344/452 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers

PIC16(L)F1938/9
27.9 LCD Waveform Generation
LCD waveforms are generated so 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 it 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 waveform:
Type-A and Type-B. In Type-A waveform, the phase
changes within each common type, whereas in Type-B
waveform, the phase changes on each frame
boundary. Thus, Type-A waveform maintains 0 VDC
over a single frame, whereas Type-B waveform takes
two frames.
Note 1: If Sleep has to be executed with LCD
Sleep disabled (LCDCON<SLPEN> is
‘1’), then care must be taken to execute
Sleep only when VDC on all the pixels is
‘0’.
2: When the LCD clock source is FOSC/256,
if Sleep is executed, irrespective of the
LCDCON<SLPEN> setting, the LCD
immediately goes into Sleep. Thus, take
care to see that VDC on all pixels is ‘0’
when Sleep is executed.
Figure 27-8 through Figure 27-18 provide waveforms
for static, half-multiplex, 1/3-multiplex and 1/4-multiplex
drives for Type-A and Type-B waveforms.
FIGURE 27-8:
TYPE-A/TYPE-B WAVEFORMS IN STATIC DRIVE
V₁
COM0 pin
COM0
V₀
V₁
SEG0 pin
V₀
V₁
SEG1 pin
V₀
V₁
COM0-SEG0
V₀
segment voltage
(active)
-V₁
COM0-SEG1
V₀
segment voltage
(inactive)
1 Frame
DS41574A-page 344
Preliminary
 2011 Microchip Technology Inc.