Atmel AVR1923

11

8394B-AVR-02/12

Display voltage (contrast control).

⎟

⎠

⎞

⎜

⎝

⎛ +

Ra

Rb

1

: Voltage regulator internal resistance ratio.

Internal fixed voltage supply typically 2.1V.

α:

Electronic volume level, 1 to 64 are possible values:

The recommended configuration for the display is to use

5

.

3

1

=

⎟

⎠

⎞

⎜

⎝

⎛ +

Ra

Rb

because it

will center the adjustable voltage range at 6V which is the typical setting for this

display. Recommended values for α are listed in Table 5-6.

Table 5-6. Recommended electronic volume configuration.

Electronic volume

register value (α)

Contrast

20

6.44

Too strong contrast

21

6.40

22

6.35

23

6.31

24

6.26

25

6.22

26

6.17

27

6.13

28

6.08

29

6.03

30

5.99

Optimal setting

31

5.94

32

5.90

33

5.85

34

5.81

35

5.76

36

5.72

37

5.67

38

5.63

39

5.58

40

5.54

Very weak contrast

The display backlight is controlled by a FET which is by default in an off state but it is

possible to turn the backlight on with the Atmel AVR XMEGA by driving the gate of

the FET high. On the XMEGA pin PE4 is connected to the gate of the FET. The pin

PE4 is also an output of an on-chip timer module and because of that it is easy to do

dimming of the backlight by using PWM.