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TM1637Six-digit LED driver with key scanning

Two control wires. Six digit positions. A built-in key scanner.

Manufacturer-referenced

Titan Micro Electronics · TM1637

DIP-20TM1637 · V2.4

TM1637 integrates a six-digit LED driver, six bytes of display RAM and a 16-key scanner in a 20-pin IC. It drives common-anode displays: GRID outputs source the digit current and SEG outputs sink the individual segment currents. A host updates the display through CLK and bidirectional DIO. The interface resembles I²C electrically, but it has no slave address and transfers each byte least-significant bit first. The host must release DIO for the acknowledgement clock. This reference covers the DIP-20 and SOP-20 packages in Titan Micro V2.4. Its example uses a 5 V host, six digits, two 10 kΩ pull-ups and local supply bypassing. Eight non-linear PWM settings adjust brightness; digit bytes directly select segments rather than decoding decimal numbers.

Real View

TM1637 black DIP-20 package with silver contacts and readable marking.
TM1637 · DIP-20Package illustration

Pinout

TM1637DIP-20Top view
Select a pin to see its functionDIP-20 · 20 pins

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20Physical pins TM1637DIP-20 Manufacturer-referencedTitan Micro Electronics

Pin diagram

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Package map
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TM1637DIP-20Top view

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1
PIN 1 · Ground

GND

Ground

Function

Supply and segment-current return.

How to connect

Connect to the common ground and the bypass capacitors.

Key specifications

The host writes one segment byte per grid position. The internal oscillator scans the digits, PWM controls brightness and the shared segment outputs also scan the optional key matrix.

Display capacity6 digits × 8 segments
Example supply5 V
Key matrix16 keys · one reported at a time
PWM settings8 non-linear levels

Operating profile

Supply, signals and operating conditions

TM1637 operating profile
ParameterValueConditions / notes
PackageDIP-2020 leads · common physical numbering
Operating temperature−40 to +85°CCheck dissipation and display current
Serial example100 kHzLSB first · START / STOP / ACK
Use these values with the stated grade and test conditions.

Package details

TM1637 · DIP-20

Selected package
Selected TM1637 physical package
PropertyDetails
ManufacturerTitan Micro Electronics
Part numberTM1637
PackageDIP-20
Connections20 pins
MountingThrough-hole
Lead pitch2.54 mm
Package codeDIP-20
Thermal referenceSee operating and package limits

Supply and electrical conditions

Distinguish operating conditions from absolute limits

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ParameterValueConditions / notes
Nominal application supply5 VV2.4 reference circuit
Electrical/timing test supply4.5–5.5 VPublished characteristics use this range
Input HIGH / LOW≥0.7 × VDD / ≤0.3 × VDDAt 5 V: ≥3.5 V HIGH, ≤1.5 V LOW
Operating temperature−40 to +85°CBoard and LED heating must remain within limits
No-load current, display OFF5 mA maximumNot total LED supply current
Internal oscillator450 kHz typicalRC oscillator; display scan is automatic
Bypass example100 nF ceramic + 100 µF bulkPlace close to VDD16 / GND1
Absolute limits7 V supply; 400 mW dissipationDamage limits, not recommended operating settings

Use a compatible host or proper level translation; a 3.3 V HIGH is not guaranteed at a 5 V supply.

Display and key commands

Each command byte is sent LSB first

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ParameterValueConditions / notes
0x40Write display, auto incrementNormal mode; addresses advance through six bytes
0x44Write display, fixed addressSend the chosen address and one byte
0x42Read key-scan codeRelease DIO for IC-to-host transfer
0xC0–0xC5Set display addressGRID1 through GRID6 respectively
0xC6 and higherOutside display RAMData ignored until a valid address is selected
0x80Display OFFOutput blanking command
0x88–0x8FDisplay ON + brightnessLow three bits select the PWM setting
Test mode bitKeep clearedReserved for manufacturer testing

There is no I²C slave address or decimal-to-segment decoder.

Segment bytes and example digits

Example wiring: SEG1…SEG8 = A, B, C, D, E, F, G, DP

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ParameterValueConditions / notes
Byte D0…D7SEG1…SEG8A set bit enables its segment
Blank / dash0x00 / 0x40Dash uses only segment G
Digits 0, 1, 2, 30x3F, 0x06, 0x5B, 0x4FFor the stated segment wiring
Digits 4, 5, 6, 70x66, 0x6D, 0x7D, 0x07No automatic font decoding
Digits 8, 90x7F, 0x6FDecimal point remains off
Decimal pointOR the byte with 0x80Some modules wire this output to a colon instead
Six-digit example 12345606 5B 4F 66 6D 7DSend after 0xC0 with auto increment enabled

A breakout module can have a different digit or colon map; check its wiring.

Eight PWM brightness settings

Duty applies during the selected digit slot

Scroll sideways to see all columns.

ParameterValueConditions / notes
0x88 / level 01/16Display ON; minimum PWM
0x89 / level 12/16
0x8A / level 24/16
0x8B / level 310/16The step from level 2 is intentionally large
0x8C / level 411/16
0x8D / level 512/16
0x8E / level 613/16
0x8F / level 714/16Maximum PWM setting

PWM duty is not the complete per-LED average duty: digit multiplexing also applies.

Two-wire timing

Use the conservative 100 kHz example for both writing and key reads

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ParameterValueConditions / notes
START / STOPDIO falls / rises while CLK HIGHKeep DIO stable during ordinary HIGH clock periods
Bit orderLeast-significant bit firstDifferent from many SPI devices
AcknowledgeNinth clock; DIO pulled LOWHost releases DIO after bit 7
Write clock upper specification500 kHz at 50% dutyElectrical table maximum, subject to timing limits
Key-read clockBelow 250 kHzAdditional instruction in the key-read section
Clock pulse widthAt least 400 nsObserve all other timing constraints too
Data setup / holdAt least 100 ns / 100 nsRelative to CLK
Waiting timeAt least 1 µsCLK rising to falling in the timing table

The 100 kHz demonstration provides margin for pull-ups, wiring capacitance and host timing.

Key scan and output loading

Optional 8 × 2 matrix shares the segment scan lines

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ParameterValueConditions / notes
K1 / K2 contactsPins 19 / 20Two key-return inputs
Idle key code0xFFNo key reported
Simultaneous keysNot supportedDo not assume rollover or independent key bits
Key input bias10 kΩ nominal internal pull-downUnused K1/K2 can remain unconnected
Segment sink capability20 / 30 / 50 mA min / typ / maxAt VO=0.3 V in the electrical table
Grid source capability80 / 120 / 180 mA min / typ / maxAt VO=VDD−2 V
Current interpretationThese are output-characteristic test valuesNot a guaranteed constant-current setting or a free current budget
Display loadingCheck LED pulse limits and IC dissipationUse segment resistors when required by the selected display/current design

Unlike MAX7219, TM1637 has no external RSET pin; do not copy the MAX7219 current-setting circuit.

Connections by function

Select a pin for its function, connection guidance and electrical notes.

Ground1 pin

Segments / key scan8 pins

Common-anode digits6 pins

Supply1 pin

Two-wire controls2 pins

Key inputs2 pins

Read the conditions with every value

Typical values describe stated test conditions. Absolute maximum ratings are stress limits, not operating targets.

Official PDF datasheet

TM1637 at a glance

Follow the labeled connections and functional stages

TM1637 working principle: illustrated functional stages, basic circuit and connections
Select the diagram to read it at full resolution.

How it works

3 stages · Explore one step at a time

Step 1 / 3

Connect a common-anode display

GRID1–GRID6 feed the digit anodes; SEG1–SEG8 sink the corresponding segment cathodes.

Step 2 / 3

Write segment patterns

Choose sequential or fixed-address writes and acknowledge each byte.

Step 3 / 3

Set brightness and read keys

Display control selects one of eight PWM duties; 0x42 requests key data.

TM1637 in a circuit

5 V host, bidirectional data, pull-ups and local bypassing.

Physical TM1637 DIP20 and six common-anode digits, shared segment cathodes, distinct grid anodes, 10k pull-ups and supply bypass capacitors.
Matching net names connect; each display bus represents separate wires. Optional segment resistors must be selected for the actual LED and pulse-current limits.

Connect it, step by step

Follow the component values and pin connections

Power and bypass

Use regulated 5 V, common ground, 100 nF and 100 µF near the IC.

Release DIO for ACK

Pull CLK and DIO up through 10 kΩ and use a compatible host.

Write and enable

Write the six display bytes with 0x40 / 0xC0, then enable with 0x8B. K1/K2 are unused in this example.

Inside TM1637

Compact functional view of serial, display and key-scan blocks.

TM1637 functional blocks within a silver-leaded IC: serial interface, command decoder, six-byte RAM, oscillator, PWM, segment/grid drivers and key scan.
Original functional illustration; not a transistor-level die schematic.

Explore the circuit

Select a stage to see its role and connections

Receive and acknowledge

The two-wire front end recognizes START, bytes, ACK and STOP.

Store display bytes

Six RAM addresses retain raw segment patterns.

Scan LEDs and keys

Grid timing, segment sinks and the key returns work from the internal oscillator.

Selected packageDIP-20TM1637
Physical connections20 pinsPackage-specific numbering
Reference collection7 tables47 parameters & pin functions

Pin reference

Signal names, electrical functions and connection guidance

DIP-20
Physical pin numbers20 pins

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TM1637 pin functions and connections
PinSignalTypeFunction & connection
GNDGroundSupply and segment-current return.
Connection guidance

Connect to the common ground and the bypass capacitors.

SEG1 / KS1Open-drain sink / scanSinks current from segment 1; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment A across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG2 / KS2Open-drain sink / scanSinks current from segment 2; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment B across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG3 / KS3Open-drain sink / scanSinks current from segment 3; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment C across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG4 / KS4Open-drain sink / scanSinks current from segment 4; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment D across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG5 / KS5Open-drain sink / scanSinks current from segment 5; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment E across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG6 / KS6Open-drain sink / scanSinks current from segment 6; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment F across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG7 / KS7Open-drain sink / scanSinks current from segment 7; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment G across the display.

A set display bit enables the corresponding sink during the selected grid slot.

SEG8 / KS8Open-drain sink / scanSinks current from segment 8; also provides key-scan timing.
Connection guidance

Connect to the shared cathodes of segment DP across the display.

A set display bit enables the corresponding sink during the selected grid slot.

GRID6High-side sourceDrives the common anode of digit 6.
Connection guidance

Connect to the common anode of display digit 6.

Use common-anode LEDs; these outputs are not logic-level GPIO.

GRID5High-side sourceDrives the common anode of digit 5.
Connection guidance

Connect to the common anode of display digit 5.

Use common-anode LEDs; these outputs are not logic-level GPIO.

GRID4High-side sourceDrives the common anode of digit 4.
Connection guidance

Connect to the common anode of display digit 4.

Use common-anode LEDs; these outputs are not logic-level GPIO.

GRID3High-side sourceDrives the common anode of digit 3.
Connection guidance

Connect to the common anode of display digit 3.

Use common-anode LEDs; these outputs are not logic-level GPIO.

GRID2High-side sourceDrives the common anode of digit 2.
Connection guidance

Connect to the common anode of display digit 2.

Use common-anode LEDs; these outputs are not logic-level GPIO.

GRID1High-side sourceDrives the common anode of digit 1.
Connection guidance

Connect to the common anode of display digit 1.

Use common-anode LEDs; these outputs are not logic-level GPIO.

VDDSupplyPowers the logic and display drivers.
Connection guidance

The example uses a regulated 5 V rail with 100 nF and 100 µF bypass near the IC.

Electrical and timing characteristics are specified at 4.5–5.5 V; follow the purchased part revision.

DIOBidirectional dataTransfers command, display and key bytes; the IC pulls this line LOW for acknowledgement.
Connection guidance

Use a 10 kΩ pull-up to 5 V and an open-drain or releasable host pin.

Release the line for the ninth ACK clock and when reading keys; never contend with the IC output.

CLKClock inputClocks data on rising edges.
Connection guidance

Use a 10 kΩ pull-up to 5 V; the example host clocks at 100 kHz.

This two-wire protocol is not I²C: no slave address, and bytes are sent least-significant bit first.

K1Key inputFirst row input for the 8 × 2 key matrix.
Connection guidance

Optional keys connect to the SEG/KS scan lines as shown in the manufacturer circuit.

Internal nominal 10 kΩ pull-down; leave unused key inputs unconnected.

K2Key inputSecond row input for the 8 × 2 key matrix.
Connection guidance

Read with command 0x42; one key code is returned.

Combined key presses are not supported; idle key data is 0xFF.

DIP-20 · Top view · Select a pin number to open its interactive pinout.

Supply and electrical conditions

Distinguish operating conditions from absolute limits

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
Nominal application supply5 VV2.4 reference circuit
Electrical/timing test supply4.5–5.5 VPublished characteristics use this range
Input HIGH / LOW≥0.7 × VDD / ≤0.3 × VDDAt 5 V: ≥3.5 V HIGH, ≤1.5 V LOW
Operating temperature−40 to +85°CBoard and LED heating must remain within limits
No-load current, display OFF5 mA maximumNot total LED supply current
Internal oscillator450 kHz typicalRC oscillator; display scan is automatic
Bypass example100 nF ceramic + 100 µF bulkPlace close to VDD16 / GND1
Absolute limits7 V supply; 400 mW dissipationDamage limits, not recommended operating settings

Use a compatible host or proper level translation; a 3.3 V HIGH is not guaranteed at a 5 V supply.

Display and key commands

Each command byte is sent LSB first

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
0x40Write display, auto incrementNormal mode; addresses advance through six bytes
0x44Write display, fixed addressSend the chosen address and one byte
0x42Read key-scan codeRelease DIO for IC-to-host transfer
0xC0–0xC5Set display addressGRID1 through GRID6 respectively
0xC6 and higherOutside display RAMData ignored until a valid address is selected
0x80Display OFFOutput blanking command
0x88–0x8FDisplay ON + brightnessLow three bits select the PWM setting
Test mode bitKeep clearedReserved for manufacturer testing

There is no I²C slave address or decimal-to-segment decoder.

Segment bytes and example digits

Example wiring: SEG1…SEG8 = A, B, C, D, E, F, G, DP

Manufacturer-referenced values7 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
Byte D0…D7SEG1…SEG8A set bit enables its segment
Blank / dash0x00 / 0x40Dash uses only segment G
Digits 0, 1, 2, 30x3F, 0x06, 0x5B, 0x4FFor the stated segment wiring
Digits 4, 5, 6, 70x66, 0x6D, 0x7D, 0x07No automatic font decoding
Digits 8, 90x7F, 0x6FDecimal point remains off
Decimal pointOR the byte with 0x80Some modules wire this output to a colon instead
Six-digit example 12345606 5B 4F 66 6D 7DSend after 0xC0 with auto increment enabled

A breakout module can have a different digit or colon map; check its wiring.

Eight PWM brightness settings

Duty applies during the selected digit slot

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
0x88 / level 01/16Display ON; minimum PWM
0x89 / level 12/16
0x8A / level 24/16
0x8B / level 310/16The step from level 2 is intentionally large
0x8C / level 411/16
0x8D / level 512/16
0x8E / level 613/16
0x8F / level 714/16Maximum PWM setting

PWM duty is not the complete per-LED average duty: digit multiplexing also applies.

Two-wire timing

Use the conservative 100 kHz example for both writing and key reads

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
START / STOPDIO falls / rises while CLK HIGHKeep DIO stable during ordinary HIGH clock periods
Bit orderLeast-significant bit firstDifferent from many SPI devices
AcknowledgeNinth clock; DIO pulled LOWHost releases DIO after bit 7
Write clock upper specification500 kHz at 50% dutyElectrical table maximum, subject to timing limits
Key-read clockBelow 250 kHzAdditional instruction in the key-read section
Clock pulse widthAt least 400 nsObserve all other timing constraints too
Data setup / holdAt least 100 ns / 100 nsRelative to CLK
Waiting timeAt least 1 µsCLK rising to falling in the timing table

The 100 kHz demonstration provides margin for pull-ups, wiring capacitance and host timing.

Key scan and output loading

Optional 8 × 2 matrix shares the segment scan lines

Manufacturer-referenced values8 parameters

Scroll within the table to see all columns and rows.

ParameterValueConditions / notes
K1 / K2 contactsPins 19 / 20Two key-return inputs
Idle key code0xFFNo key reported
Simultaneous keysNot supportedDo not assume rollover or independent key bits
Key input bias10 kΩ nominal internal pull-downUnused K1/K2 can remain unconnected
Segment sink capability20 / 30 / 50 mA min / typ / maxAt VO=0.3 V in the electrical table
Grid source capability80 / 120 / 180 mA min / typ / maxAt VO=VDD−2 V
Current interpretationThese are output-characteristic test valuesNot a guaranteed constant-current setting or a free current budget
Display loadingCheck LED pulse limits and IC dissipationUse segment resistors when required by the selected display/current design

Unlike MAX7219, TM1637 has no external RSET pin; do not copy the MAX7219 current-setting circuit.

Read each value with its conditions

Typical values describe the stated test conditions. Absolute maximum ratings are stress limits, not operating targets.

Titan Micro Electronics · TM1637 · V2.4
Official PDF datasheet

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