AS1108
Datasheet - Detailed Description
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.
Table 14. Intensity Register Format (Address (HEX) = 0xXA))
Duty Cycle
AS1108
1/32 (min on)
3/32
Register Data
HEX Code
D7
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D6
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D5
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D4
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
D2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
D1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
D0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0xX0
0xX1
0xX2
0xX3
0xX4
0xX5
0xX6
0xX7
0xX8
0xX9
0xXA
0xXB
0xXC
0xXD
0xXE
0xXF
5/32
7/32
9/32
11/32
13/32
15/32
17/32
19/32
21/32
23/32
25/32
27/32
29/32
31/32 (max on)
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 15. Scan-Limit Register Format (Address (HEX) = 0xXB))
Register Data
Scan Limit
HEX Code
D7
X
X
X
X
D6
X
X
X
X
D5
X
X
X
X
D4
X
D3
X
D2
0
D1
0
D0
0
Display digit 0 only (see Table 16)
Display digits 0:1 (see Table 16)
Display digits 0:2 (see Table 16)
Display digits 0:3
0xX0
0xX1
0xX2
0xX3
X
X
0
0
1
X
X
0
1
0
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
2
3
10
20
30
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