Analog Devices (Maxim) · Integrated circuit

MAX7219 LED Display Driver

Drives eight 7-segment digits or an 8x8 matrix over three wires, with its own BCD decoder, brightness control and scanning. No refresh code at all.

1.Pinout diagram

Pins 1-12

MAX7219

Pins 13-24

Pin detail

Hover a pin for its mappings and gotchas. Click to keep it here.

Fig. 1. MAX7219 LED Display Driver, PDIP-24. Hover or tap a signal to light up every pin that carries it.

Both GND pins, 4 and 9, must be connected. Wiring only one works on the bench and then flickers.
ISET takes a resistor to V+, not to ground. That resistor sets peak segment current: around 10k for 40 mA, 28k for about 20 mA. Leaving it open means no light; shorting it destroys the chip.
It scans the digits itself at about 800 Hz and holds the data, so you write once and walk away. There is no refresh loop to run.
The digit and segment pins are scattered around the package in no sensible order. A matrix wired by eye instead of by pin number comes out transposed or mirrored, which is the single most common MAX7219 complaint.
Brightness is both digital, 16 steps over SPI, and analog through ISET. Set the coarse level with the resistor and trim in software.
Decode mode turns raw segment control into BCD digits per position. Turn it off for a matrix or for custom glyphs, on for numeric displays.
The MAX7221 is the same part with SPI-compliant timing and slew-limited segment drivers for less RFI. It also respects CS properly, which matters on a shared bus.
Peak current across all eight digits can reach 330 mA. The cheap modules do not decouple well; add 100 uF if the display dims as digits light.

What has to go around the chip before it will run.

Fig. 2. Minimum circuit, drawn from Table 1. Crossing wires are not connected.

Table 1. External parts, and why each one is there.
Part	Between	Why
12 kOhm	ISET (18) to VCC	RSET sets the peak segment current, about 100 times the ISET current. Table 11 of the datasheet gives 11.8 kOhm for 40 mA into a 2 V LED.
10 uF	V+ (19) to GND	The datasheet asks for this next to the part. Scanning digits pull current in hard bursts.
100 nF	V+ (19) to GND	The ceramic half of the same job, as close to the pin as it will go.

Both GND pins, 4 and 9, must be connected. 40 mA per segment is the recommended maximum; above that you need external digit drivers.

Every pin, alias and mapping. This is the table that prints.

Table 2. Pin assignments.

Complete pin reference for MAX7219 LED Display Driver
Pin	Name	Also called	Functions	Notes
1	DINSPI	-	Serial data in	This is MOSI. Sampled on the rising edge of CLK.
2	DIG0	-	Digit 0 drive	Digit drivers are scattered across the package in no useful order. Wire from the numbers.
3	DIG4	-	Digit 4 drive
4	GND	-	Ground	Both ground pins, 4 and 9, must be connected. One is not enough.
5	DIG6	-	Digit 6 drive
6	DIG2	-	Digit 2 drive
7	DIG3	-	Digit 3 drive
8	DIG7	-	Digit 7 drive
9	GND	-	Ground	The second ground. Connect it.
10	DIG5	-	Digit 5 drive
11	DIG1	-	Digit 1 drive
12	LOADSPI	CS, /CS	Load / chip select	Rising edge latches the last 16 bits. This is CS.
13	CLKSPIClock	-	Serial clock	10 MHz maximum. This is SCK.
14	SEG A	-	Segment A drive
15	SEG F	-	Segment F drive	Segment order on the package is scrambled too: A, F, B, G down this side.
16	SEG B	-	Segment B drive
17	SEG G	-	Segment G drive
18	ISET	-	Peak current set	A resistor from here to V+ sets segment current. 10k gives roughly 40 mA per segment; never leave it open or short it.
19	V+4.0-5.5 V	-	Positive supply	5 V. Needs 10 uF and 100 nF right at the pin; eight digits strobing is a hard load.
20	SEG C	-	Segment C drive
21	SEG E	-	Segment E drive
22	SEG DP	DP	Decimal point drive
23	SEG D	-	Segment D drive
24	DOUTSPI	-	Serial data out	Feed into the next chip's DIN to chain displays. Data appears 16.5 clocks later.

Found a wrong pin? The whole board is one file, data/boards/max7219.json.