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AS1105

Datasheet - Detailed Descr i p ti on

8.4 Initial Power-up

After powering up the system, all register are reset, so that the display is blank. The AS1105 starts the shutdown mode. All registers should be

programmed for normal operation. The default settings enable only scan of one digit, the internal decoder is disabled, data register and intensity

register are set to the minimum value.

8.5 Decode-Mode Register

In the AS1105, a BCD decoder is included. Every digit can be selected via register 09h to be decoded. The BCD code consists of the numbers 0-

9, E,H, L,P and -. In register 09h, a logic high enables the decoder for the appropriate digit. In case that the decoder is bypassed (logic low), the

data Bits D7-D0 correspond to the segment lines of the AS1105. In Table 7 some possible settings for register 09h are shown. Bit D7, which

corresponds to the decimal point, is not affected by the settings of the decoder. Logic high means that the decimal point is displayed. In Table 8

the font of the Code B decoder is shown. In Table 10 the correspondence of the register to the appropriate segments of a 7 segment display is

shown (see Figure 6).

8.6 Intensity Control and Interdigit Blanking

Brightness of the display can be controlled in an analog way by changing the external resistor (RSET). The current, which flows between VDD

and ISET, defines the current that flows through the LEDs. The LED current is 100 times the ISET current. The minimum value of RSET should be

9.53k

Ω, which corresponds to 40mA segment current. The brightness of the display can also be controlled digitally via register 0Ah. The

brightness can be programmed in 16 steps and is shown in Table 10. An internal pulse width modulator controls the intensity of the display.

8.7 Scan-Limit Register

The scan limit register 0Bh selects the number of digits displayed. When all 4 digits are displayed the update frequency is typically 800Hz. If the

number of digits displayed is reduced, the update frequency is reduced as well. The frequency can be calculated using 8fOSC/N, where N is the

number of digits. Since the number of displayed digits influences the brightness, the resistor RSET should be adjusted accordingly. Table 12

shows the maximum allowed current, when fewer than 4 digits are used. To avoid differences in brightness the scan limit register should not be

used to blank portions of the display (leading zeros).

Table 5. Register Address Map

Register

Register

Hex Code

D15-D12

D11

D10

D9

D8

No-Op

X

0

0

0

0

0xX0

Digit 0

X

0

0

0

1

0xX1

Digit 1

X

0

0

1

0

0xX2

Digit 2

X

0

0

1

1

0xX3

Digit 3

X

0

1

0

0

0xX4

Decode Mode

X

1

0

0

1

0xX9

Intensity

X

1

0

1

0

0xXA

Scan Limit

X

1

0

1

1

0xXB

Shutdown

X

1

1

0

0

0xXC

Not used

X

1

1

0

1

0xXD

Reset and ext. Clock

X

1

1

1

0

0xXE

Display Test

X

1

1

1

1

0xXF