W79E217A Datasheet, PDF (172/207 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E217A Data Sheet
LCD frequency is set by the LCDCN.FS [2:0] register bits. LCDEN (LCDCN.7) can enable or disable
the LCD by software. If LCDEN is set, voltage pump supplies voltage to segment and com drivers and
LCD panel will be displayed according LCDDATA. See below section for explanation. When LCDEN is
clear, voltage pump is turn off and all LCD pins will be output at LOW. Pump (LCDCN.4) can select
which voltage pump (Type A or B) to drive Segments and Com. Default is pump type A which is
normal mode, while pump Type B is power saving mode. The duty cycles are selectable at LCDCN.5
for 32*4 dots is ¼ duty and 32*3 dots is 1/3 duty. There is a CLEAR bit (LCDCN.6) for clearing the
LCD display and by default it is inactive. Upon activating this CLEAR bit the COM pin will goes LOW
that will directly clear the LCD displayed. However, when the CLEAR bit is deactivated again by
software, the LCD display will resume previous display prior to clear.
20.2 LCD Frequency
LCD frequency can be set by FS [2:0] bits. Setting a correct frequency according to the LCD panel
requirement will get a good contrast. Structure of the LCD frequency selection block (FLCD) is shown
in the following diagram Figure 20-2.
Figure 20-2: LCD frequency selection block diagram (FLCD)
FS2
FS1
FS0
0
0
0
0
0
1
0
1
0
0
1
1
1
x
x
DIVIDER
/1
/2
/4
/8
/16
Table 20-1: Divider selection table using FS bits
User is free to select any LCD frequency by selecting the divider. The LCD frequency can be
calculated by following equation:
LCD frequency (FLCD) = (Fosc/2*14) X (Divider)
Each common signal is selected sequentially according to the specified number of time slices of its
frame period. For example, in 1/3 duty, COM0 to COM2 will output waveforms, COM3 will be tied to
low. Whereas for 1/4 duty, COM0 to COM3 will output waveforms. Refer to the figure below.
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Publication Release Date: December 14, 2007
Revision A3.0