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Revision 2.13

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AS1108

Datasheet - D e t a i l e d D e s c r i p t i o n

Intensity Control Register (0xXA)

The brightness of the display can be controlled by digital means using the Intensity Control Register and by analog

means using RSET (see Selecting RSET Resistor Value and Using External Drivers on page 14).

Display brightness is controlled by an integrated pulse-width modulator which is controlled by the lower-nibble of the

Intensity Control Register. The modulator scales the average segment-current in 16 steps from a maximum of 31/32

down to 1/32 of the peak current set by RSET.

Scan-Limit Register (0x0B)

The Scan-Limit Register controls which of the digits are to be displayed. When all 4 digits are to be displayed, the

update frequency is typically 1600Hz. If the number of digits displayed is reduced, the update frequency is increased.

The frequency can be calculated using 8fOSC/N, where N is the number of digits. Since the number of displayed digits

influences the brightness, RSET should be adjusted accordingly. Table 16 lists the maximum allowed current when

fewer than 4 digits are used.

Note: To avoid differences in brightness this register should not be used to blank parts of the display (leading zeros).

Table 14. Intensity Register Format (Address (HEX) = 0xXA))

Duty Cycle

HEX Code

Register Data

AS1108

D7

D6

D5

D4

D3

D2

D1

D0

1/32 (min on)

0xX0

X

X

X

X

0

0

0

0

3/32

0xX1

X

X

X

X

0

0

0

1

5/32

0xX2

X

X

X

X

0

0

1

0

7/32

0xX3

X

X

X

X

0

0

1

1

9/32

0xX4

X

X

X

X

0

1

0

0

11/32

0xX5

X

X

X

X

0

1

0

1

13/32

0xX6

X

X

X

X

0

1

1

0

15/32

0xX7

X

X

X

X

0

1

1

1

17/32

0xX8

X

X

X

X

1

0

0

0

19/32

0xX9

X

X

X

X

1

0

0

1

21/32

0xXA

X

X

X

X

1

0

1

0

23/32

0xXB

X

X

X

X

1

0

1

1

25/32

0xXC

X

X

X

X

1

1

0

0

27/32

0xXD

X

X

X

X

1

1

0

1

29/32

0xXE

X

X

X

X

1

1

1

0

31/32 (max on)

0xXF

X

X

X

X

1

1

1

1

Table 15. Scan-Limit Register Format (Address (HEX) = 0xXB))

Scan Limit

HEX Code

Register Data

D7

D6

D5

D4

D3

D2

D1

D0

Display digit 0 only (see Table 16)

0xX0

X

X

X

X

X

0

0

0

Display digits 0:1 (see Table 16)

0xX1

X

X

X

X

X

0

0

1

Display digits 0:2 (see Table 16)

0xX2

X

X

X

X

X

0

1

0

Display digits 0:3

0xX3

X

X

X

X

X

0

1

1

Table 16. Maximum Segment Current for 1-, 2-, or 3-Digit Displays

Number of Digits Displayed

Maximum Segment Current (mA)

1

10

2

20

3

30