Serially Interfaced, 8-Digit LED Display Drivers
Table 2. Register Address Map
ADDRESS
REGISTER
No-Op
Digit 0
Digit 1
Digit 2
Digit 3
Digit 4
Digit 5
Digit 6
Digit 7
Decode
Mode
Intensity
Scan Limit
Shutdown
Display
Test
D15–
D12
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D11
0
0
0
0
0
0
0
0
1
1
1
1
1
1
D10
0
0
0
0
1
1
1
1
0
0
0
0
1
1
D9
0
0
1
1
0
0
1
1
0
0
1
1
0
1
D8
0
1
0
1
0
1
0
1
0
1
0
1
0
1
HEX
CODE
0xX0
0xX1
0xX2
0xX3
0xX4
0xX5
0xX6
0xX7
0xX8
0xX9
0xXA
0xXB
0xXC
0xXF
Initial Power-Up
On initial power-up, all control registers are reset, the
display is blanked, and the MAX7219/MAX7221 enter
shutdown mode. Program the display driver prior to
display use. Otherwise, it will initially be set to scan one
digit, it will not decode data in the data registers, and
the intensity register will be set to its minimum value.
MAX7219/MAX7221
Decode-Mode Register
The decode-mode register sets BCD code B (0-9, E, H,
L, P, and -) or no-decode operation for each digit. Each
bit in the register corresponds to one digit. A logic high
selects code B decoding while logic low bypasses the
decoder. Examples of the decode mode control-regis-
ter format are shown in Table 4.
When the code B decode mode is used, the decoder
looks only at the lower nibble of the data in the digit
registers (D3–D0), disregarding bits D4–D6. D7, which
sets the decimal point (SEG DP), is independent of the
decoder and is positive logic (D7 = 1 turns the decimal
point on). Table 5 lists the code B font.
When no-decode is selected, data bits D7–D0 corre-
spond to the segment lines of the MAX7219/MAX7221.
Table 6 shows the one-to-one pairing of each data bit
to the appropriate segment line.
Table 3. Shutdown Register Format (Address (Hex) = 0xXC)
REGISTER DATA
MODE
Shutdown
Mode
Normal
Operation
ADDRESS CODE
(HEX)
0xXC
0xXC
D7
X
X
D6
X
X
D5
X
X
D4
X
X
D3
X
X
D2
X
X
D1
X
X
D0
0
1
Table 4. Decode-Mode Register Examples (Address (Hex) = 0xX9)
DECODE MODE
No decode for digits 7–0
Code B decode for digit 0
No decode for digits 7–1
Code B decode for digits 3–0
No decode for digits 7–4
Code B decode for digits 7–0
REGISTER DATA
D7
0
0
0
1
D6
0
0
0
1
D5
0
0
0
1
D4
0
0
0
1
D3
0
0
1
1
D2
0
0
1
1
D1
0
0
1
1
D0
0
1
1
1
HEX
CODE
0x00
0x01
0x0F
0xFF
7
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