AS8218 datasheet(48/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 48 of 123

8.2

LCD Driver (LCDD)

LCD

Drive

Voltage

Level

Generation

VREG

LBP0

LBP1

LBP2

LBP3

LSD0

LSD23

selvlcd

VDD

VSS

MCU

LCDD

Control

Data

Register1

Data

Register2

lcdd_pd

Figure 6:

LCD driver block diagram

The on-chip LCD driver (LCDD) is a peripheral block, which interfaces to almost any liquid crystal display

(LCD) having a multiplex rate of 4. It generates the drive signals to directly drive multiplexed LCDs containing

up to four backplanes and up to 24 segments per backplane. The AS8218 has a 20 x 4 LCDD, while the

AS8228 has a 24 x 4 LCDD.

The data registers receive and store the display information, which is to be sent to the display. The LCDD

control block decodes the information into the select lines for the single segments using a specific timing.

The LCD voltage can be selected to adjust the contrast of the display, as required. The selvlcd[2:0] register

bits enable the setting of the LCD contrast by selecting one of the defined LCD voltage levels. The contrast can

be improved with a higher voltage, however the contrast is also dependent upon the crystal frequency.

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