AS1100 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS1100

Serially Interfaced, 8-Digit LED Driver

austriamicrosystems AG 

Data Sheet AS1100

Display Test Register

With the display test register 0Fh all LED can be tested. In

the test mode all LEDs are switched on at maximum

brightness (duty cycle 31/32). All programming of digit and

control registers is maintained. The format of the register is

given in table 10.

Number of

Digits

Displayed

1

2

3

Maximum

Segment Current

(mA)

10

20

30

Table 9: Maximum segment current for 1-, 2-, or 3-digit displays

Mode

Register Data

D7 D6 D5 D4 D3 D2 D1 D0

Normal Operation X X X X X X X 0

Display Test

Mode

XXXXXXX1

Table 10: Display-test register format (address (hex) = 0xXF)

Note: The AS1100 remains in display-test mode until the

display-test register is reconfigured for normal operation.

No-Op Register (Cascading of As1100)

The no-operation register 00h is used when AS1100s are

cascaded in order to support more than 8 digit displays. The

cascading must be done in a way that all DOUT are

connected to DIN of the following AS1100. The LOAD and

CLK signals are connected to all devices. For a write

operation for example to the fifth device the command must

be followed by four no-operation commands. When the

LOAD signal finally goes to high all shift registers are

latched. The first four devices have got no-operation

commands and only the fifth device sees the intended

command and updates its register.

Reset and external Clock Register3

This register is addressed via the serial interface. It allows

to switch the device to external clock mode (If D0=1 the

CLK pin of the serial interface operates as system clock

input.) and to apply an external reset (D1). This brings all

registers (except reg. E) to default state. For standard

operation the register contents should be "00h".

3 This register is not used by MAX7219, since it does not support

software reset and external clocks

Mode

Address

Register Data

code (hex) D7 D6 D5 D4 D3 D2 D1 D0

Normal Operation,

internal clock

0xXE X X X X X X 0 0

Normal Operation,

external clock

0xXE X X X X X X 0 1

Reset state,

internal clock

0xXE X X X X X X 1 0

Reset state,

external clock

0xXE X X X X X X 1 1

Table 11: Reset and external Clock register (address (hex) = 0xXE)

Applications Information

Supply Bypassing and Wiring

In order to achieve optimal performance the AS1100 shall

be placed very close to the LED display to minimize effects

of electromagnetic interference and wiring inductance.

Furthermore it is recommended to connect a 10µF

electrolytic and a 0.1µF ceramic capacitor between VDD

and GND to avoid power supply ripple. Also, both GNDs

must be connected to ground.

Selecting RSET Resistor and Using External Drivers

The current through the segments is controlled via the

external resistor RSET. Segment current is about 100 times

the current in ISET. The right values for ISET are given in

table 12. The maximum current the AS1100 can drive is

40mA. If higher currents are needed, external drivers must

be used. In that case it is no longer necessary that the

AS1100 drives high currents. A recommended value for

RSET is 47kΩ. In cases that the AS1100 only drives few

digits table 9 specifies the maximum currents and RSET must

be set accordingly. Refer to absolute maximum ratings to

calculate acceptable limits for ambient temperature,

segment current, and the LED forward-voltage drop.

ISEG (mA)

40

30

20

10

VLED (V)

1.5 2.0 2.5 3.0 3.5

12.2 11.8 11.0 10.6 9.69

17.8 17.1 15.8 15.0 14.0

29.8 28.0 25.9 24.5 22.6

66.7 63.7 59.3 55.4 51.2

Table 12: RSET vs. segment current and LED forward voltage

Revision 1.32, Oct. 2004

Page 8 of 12

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