Datasheet

Intensity Control
and Interdigit Blanking
The MAX7219/MAX7221 allow display brightness to be
controlled with an external resistor (R
SET
) connected
between V+ and ISET. The peak current sourced from
the segment drivers is nominally 100 times the current
entering ISET. This resistor can either be fixed or vari-
able to allow brightness adjustment from the front
panel. Its minimum value should be 9.53kΩ, which typi-
cally sets the segment current at 40mA. Display bright-
ness can also be controlled digitally by using the
intensity register.
Digital control of display brightness is provided by an
internal pulse-width modulator, which is controlled by
the lower nibble of the intensity 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 R
SET
(15/16 to 1/16 on MAX7221). Table 7 lists the
intensity register format. The minimum interdigit blank-
ing time is set to 1/32 of a cycle.
Serially Interfaced, 8-Digit LED Display Drivers
Table 5. Code B Font
Table 6. No-Decode Mode Data Bits and
Corresponding Segment Lines
0 0X 00 0 11 11 11
D7*
REGISTER DATA
0
7-SEGMENT
CHARACTER
D3D6–D4 D1D2 DP*D0 BA DC FE G
1 0X 00 1 10
ON SEGMENTS = 1
01 00 0
2 0X 10 0 11 10 01 1
3 0X 10 1 11 11 00 1
4 0X 01 0 10 01 10 1
5 0X 01 1 01 11 10 1
6 0X 11 0 01 11 11 1
7 0X 11 1 11 01 00 0
8 1X 00 0 11 11 11 1
9 1X 00 1 11 11 10 1
— 1X 10 0 00 00 00 1
E 1X 10 1 01 10 11 1
H 1X 01 0 10 01 11 1
L 1X 01 1 00 10 11 0
P 1X 11 0 11 00 11 1
blank 1X 11 1 00 00 00 0
* The decimal point is set by bit D7 = 1
F
E
A
G
D
C
B
STANDARD 7-SEGMENT LED
DP
A
Corresponding
Segment Line
D6
DP C
D4
B
D5
E
D2
D G
REGISTER DATA
D0
F
D1D3D7
MAX7219/MAX7221
8
Maxim Integrated