Serially Interfaced, 8-Digit LED Display Drivers
MAX7219/MAX7221
Table 5. Code B Font
7-SEGMENT
CHARACTER
0
1
2
3
4
5
6
7
8
9
—
E
H
L
P
blank
REGISTER DATA
D7*
D6–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
DP*
A
1
0
1
1
0
1
1
1
1
1
0
1
0
0
1
0
B
1
1
1
1
1
0
0
1
1
1
0
0
1
0
1
0
ON SEGMENTS = 1
C
1
1
0
1
1
1
1
1
1
1
0
0
1
0
0
0
D
1
0
1
1
0
1
1
0
1
1
0
1
0
1
0
0
E
1
0
1
0
0
0
1
0
1
0
0
1
1
1
1
0
F
1
0
0
0
1
1
1
0
1
1
0
1
1
1
1
0
G
0
0
1
1
1
1
1
0
1
1
1
1
1
0
1
0
*The decimal point is set by bit D7 = 1
Table 6. No-Decode Mode Data Bits and
Corresponding Segment Lines
A
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.
F
G
B
STANDARD 7-SEGMENT LED
E
C
D
DP
REGISTER DATA
D7
Corresponding
Segment Line
DP
D6
A
D5
B
D4
C
D3
D
D2
E
D1
F
D0
G
8
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