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.
Address
Register Data
D7 D6 D5 D4 D3 D2 D1 D0
Mode
code (hex)
Normal Operation,
internal clock
Normal Operation,
external clock
Reset state,
0xXE
0xXE
0xXE
0xXE
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
0
0
1
1
0
1
0
1
Number of
Maximum
Digits
Segment Current
internal clock
Reset state,
Displayed
(mA)
10
1
2
3
external clock
20
Table 11: Reset and external Clock register (address (hex) = 0xXE)
30
Table 9: Maximum segment current for 1-, 2-, or 3-digit displays
Applications Information
Register Data
Mode
Supply Bypassing and Wiring
D7 D6 D5 D4 D3 D2 D1 D0
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.
Normal Operation
Display Test
Mode
X
X
X
X
X
X
X
0
X
X
X
X
X
X
X
1
Furthermore it is recommended to connect
a 10µF
Table 10: Display-test register format (address (hex) = 0xXF)
electrolytic and a 0.1µF ceramic capacitor between VDD
and GND to avoid power supply ripple. Also, both GNDs
must be connected to ground.
Note: The AS1100 remains in display-test mode until the
display-test register is reconfigured for normal operation.
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.
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".
VLED (V)
ISEG (mA)
1.5
2.0
2.5
3.0
3.5
40
30
20
10
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
3
This register is not used by MAX7219, since it does not support
software reset and external clocks
Revision 1.32, Oct. 2004
Page 8 of 12
AMSCO [ AMS(艾迈斯) ]
