Preliminary

AS2591

Rev. 1.0

Page 5

May 1999

Functional Description

AS2591 is a CMOS mixed-mode integrated circuit for

driving LCDs with 4 backplanes and 24 or 31

segments providing 12 or 16 7-segment digits and 12

symbols. The device is controlled via a simple 2-wire

bus and

a

chip-select signal. The device also

includes an elapse-time counter which is started 5

seconds after power-up and incremented every

second.

The timer is re-started whenever the device gets a

WRITE-DIGIT or SHIFT&WRITE command within the

first 5 counts (except commands for displaying digits

"-", "

o

", "o"). The content of the timer is displayed 5

second

after

receiving

the

last

WRITE-DIGIT,

SHIFT&WRITE or BLINKING command. The normal

display appears immediately after receiving a WRITE-

DIGIT, SHIFT&WRITE, or BLINKING command.

Supply Arrangement

The device is supplied through V

The internal

reference voltages (V

and segment outputs are set at pin V

to 3.27V the segment output voltage is 2.97V

(middle).

This voltage can be programmed through the serial

bus to 2.83V (low) or 3.09V (high) for optimising the

contrast of the LCD. The 1/3, 2/3, and 3/3 voltages

are generated internally (see Figure 4:

Supply

arrangement). In applications with varying V

it is

recommended to insert a voltage regulator at V

order to assure a constant contrast (see also

application note AN525 for further information).

From

AS2525

Contrast

control

Contrast

control

Figure 4: Supply arrangement

LCD Digit Code

Code [HEX]:

01

02

03

04

05

06

07

08

09

00

Number:

1

2

3

4

5

6

7

8

9

0

Display:

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Code [HEX]:

0A

0B

0C

0D

0E

0F

10

11

12

13

14

Letters/Signs:

a

b

c

d

e

f

#

*

-

(

)

Display:

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Code [HEX]:

15

16

17

18

19

1A

1B

1C

1D

1E

1F

Letters/Signs:

H

I

L

N

O

P

R

T

U

"

Display: |_|

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