MAXIM MAX6956 Technical data

General Description

The MAX6956 compact, serial-interfaced LED display
driver/I/O expander provide microprocessors with up to
28 ports. Each port is individually user configurable to
either a logic input, logic output, or common-anode
(CA) LED constant-current segment driver. Each port
configured as an LED segment driver behaves as a
digitally controlled constant-current sink, with 16 equal
current steps from 1.5mA to 24mA. The LED drivers are
suitable for both discrete LEDs and CA numeric and
alphanumeric LED digits.

Each port configured as a general-purpose I/O (GPIO)
can be either a push-pull logic output capable of sink­ing 10mA and sourcing 4.5mA, or a Schmitt logic input
with optional internal pullup. Seven ports feature config­urable transition detection logic, which generates an
interrupt upon change of port logic level. The MAX6956
is controlled through an I2C™-compatible 2-wire serial
interface, and uses four-level logic to allow 16 I2C
addresses from only 2 select pins.

The MAX6956AAX and MAX6956ATL have 28 ports
and are available in 36-pin SSOP and 40-pin thin QFN
packages, respectively. The MAX6956AAI and
MAX6956ANI have 20 ports and are available in 28-pin
SSOP and 28-pin DIP packages, respectively.

For an SPI-interfaced version, refer to the MAX6957
data sheet. For a lower cost pin-compatible port
expander without the constant-current LED drive capa­bility, refer to the MAX7300 data sheet.

Applications

Set-Top Boxes Bar Graph Displays

Panel Meters Industrial Controllers

White Goods System Monitoring

Automotive

Features

♦ 400kbps I2C-Compatible Serial Interface

♦ 2.5V to 5.5V Operation

♦ -40°C to +125°C Temperature Range

♦ 20 or 28 I/O Ports, Each Configurable as

Constant-Current LED Driver
Push-Pull Logic Output
Schmitt Logic Input
Schmitt Logic Input with Internal Pullup

♦ 11µA (max) Shutdown Current

♦ 16-Step Individually Programmable Current

Control for Each LED

♦ Logic Transition Detection for Seven I/O Ports

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

________________________________________________________________ Maxim Integrated Products 1

Pin Configurations

19-2414; Rev 2; 11/03

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Typical Operating Circuit appears at end of data sheet.

Ordering Information

Purchase of I2C components of Maxim Integrated Products, Inc.,
or one of its sublicensed Associated Companies, conveys a
license under the Philips I2C Patent Rights to use these compo­nents in an I

2

C system, provided that the system conforms to the

I

2

C Standard Specification as defined by Philips.

Pin Configurations continued at end of data sheet.

PART TEMP RANGE PIN-PACKAGE

MAX6956ANI -40°C to +125°C 28 DIP

MAX6956AAI -40°C to +125°C 28 SSOP

MAX6956AAX -40°C to +125°C 36 SSOP

MAX6956ATL -40°C to +125°C 40 Thin QFN

TOP VIEW

ISET

1

GND

2

GND

3

AD0

4

P12

5

6

7

8

9

10

11

12

13

14

MAX6956

SSOP/DIP

P13

P14

P15

P16

P17

P18

P19

P20

P21

V+

28

AD1

27

SCL

26

SDA

25

P31

24

P30

23

P29

22

P28

21

P27

20

P26

19

P25

18

P24

17

P23

16

P22

15

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Voltage (with Respect to GND)

V+ .............................................................................-0.3V to +6V

SCL, SDA, AD0, AD1................................................-0.3V to +6V

All Other Pins................................................-0.3V to (V+ + 0.3V)

P4–P31 Current ................................................................±30mA

GND Current .....................................................................800mA

Continuous Power Dissipation

28-Pin PDIP (derate 20.8mW/°C above T

A

= +70°C)1667mW

28-Pin SSOP (derate 9.5mW/°C above TA= +70°C)..762mW
36-Pin SSOP (derate 11.8mW/°C above T

A

= +70°C) ..941mW

40-Pin QFN (derate 26.3mW/°C above T

A

= +70°C) ..2105mW

Operating Temperature Range

(T

MIN

to T

MAX

) ..............................................-40°C to +125°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Operating Supply Voltage V+ 2.5 5.5 V

Shutdown Supply Current I

SHDN

All digital inputs at V+
or GND

All ports programmed

Operating Supply Current I

GPOH

as outputs high, no
load, all other inputs at
V+ or GND

All ports programmed

Operating Supply Current I

GPOL

as outputs low, no
load, all other inputs at
V+ or GND

Al l p or ts p r og r am m ed

Operating Supply Current I

LED

as LE D outp uts, al l LE D s
off, no l oad , al l other
i np uts at V + or GN D T

INPUTS AND OUTPUTS

Logic-High Input Voltage
Port Inputs

Logic-Low Input Voltage
Port Inputs

Input Leakage Current IIH, I

GPIO Input Internal Pullup to V+ I

Hysteresis Voltage GPIO Inputs ∆V

V

IH

V

IL

GPIO inputs without pullup,

IL

V

V+ = 2.5V 12 19 30

PU

V+ = 5.5V 80 120 180

I

GPIO outputs, I

Output High Voltage V

OH

+85°C

GPIO outputs, I
T

Port Sink Current I

Output Short-Circuit Current I

OLSC

V

OL

Port configured output low, shorted to V+ 2.75 11 20 mA

= V+ to GND

PORT

(Note 2)

MAX

= 0.6V 2 10 18 mA

PORT

SOURCE

SOURCE

TA = +25°C 5.5 8

TA = -40°C to +85°C10

T

= T

MIN

to T

MAX

A

11

TA = +25°C 180 230

TA = -40°C to +85°C 250

T

= T

MIN

to T

MAX

A

270

TA = +25°C 170 210

TA = -40°C to +85°C 230

T

= T

MIN

to T

MAX

A

240

TA = +25°C 110 135

TA = -40°C to +85°C 140

= T

MIN

to T

MAX

0.7

✕

A

145

V+

✕

0.3
V+

-100 ±1 +100 nA

0.3 V

= 2mA, TA = -40°C to

V+ -

0.7

= 1mA, TA = T

MIN

to

V+ -

0.7

µA

µA

µA

µA

V

V

µA

V

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

_______________________________________________________________________________________ 3

Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
Note 3: A master device must provide a hold time of at least 300ns for the SDA signal (referred to V

IL

of the SCL signal) in order to

bridge the undefined region of SCL’s falling edge.

Note 4: C

b

= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.

Note 5: I

SINK

≤ 6mA. Cb= total capacitance of one bus line in pF. tRand tFmeasured between 0.3V+ and 0.7V+.

Note 6: Input filters on the SDA and SCL inputs suppress noise spikes less than 50ns.

ELECTRICAL CHARACTERISTICS (continued)

(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

TIMING CHARACTERISTICS (Figure 2)

(V+ = 2.5V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

Port Drive LED Sink Current,
Port Configured as LED Driver

Port Drive Logic Sink Current,
Port Configured as LED Driver

Input High-Voltage SDA, SCL,
AD0, AD1

Input Low-Voltage SDA, SCL,
AD0, AD1

Input Leakage Current SDA, SCL IIH, I

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

I

DIGIT

I

DIGIT_SC

V

IH

V

IL

IL

Input Capacitance (Note 2) 10 pF
Output Low-Voltage SDA V

OLISINK

V+ = 2.5V, V
current

V+ = 3.3V, V
current (Note 2)
V+ = 5.5V, V
current
V+ = 2.5V, V
current

V+ = 5.5V, V
current

= 2.3V at maximum LED

LED

= 2.4V at maximum LED

LED

= 2.4V at maximum LED

LED

= 0.6V at maximum sink

OUT

= 0.6V at maximum sink

OUT

9.5 13.5 18

18.5 24 27.5

19 25 30

18.5 23 28

19 24 28

✕

0.7
V+

0.3

-50 50 nA

= 6mA 0.4 V

✕

V+

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Serial Clock Frequency f
Bus Free Time Between a STOP
and a START Condition
Hold Time (Repeated) START
Condition
Repeated START Condition
Setup Time
STOP Condition Setup Time t
Data Hold Time t
Data Setup Time t
SCL Clock Low Period t
SCL Clock High Period t
Rise Time of Both SDA and SCL
Signals, Receiving
Fall Time of Both SDA and SCL
Signals, Receiving

Fall Time of SDA Transmitting t

Pulse Width of Spike Suppressed t
Capacitive Load for Each Bus
Line

SCL

t

BUF

t

HD, STA

t

SU, STA

SU, STO

HD, DAT

SU, DAT

LOW

HIGH

t

t

,TX

F

SP

C

(Note 3) 15 900 ns

(Notes 2, 4)

R

(Notes 2, 4)

F

(Notes 2, 5)

(Notes 2, 6) 0 50 ns

(Note 2) 400 pF

b

400 kHz

1.3 µs

0.6 µs

0.6 µs

0.6 µs

100 ns

1.3 µs

0.7 µs
20 +

0.1C
20 +

0.1C
20 +

0.1C

b

b

b

300 ns

300 ns

250 ns

mA

mA

V

V

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

4 _______________________________________________________________________________________

__________________________________________Typical Operating Characteristics

(R

ISET

= 39kΩ, TA = +25°C, unless otherwise noted.)

OPERATING SUPPLY CURRENT

vs. TEMPERATURE

0.40

V+ = 2.5V TO 5.5V

0.36

NO LOAD

0.32

0.28

ALL PORTS
OUTPUT (1)

0.24

0.20

0.16

0.12

SUPPLY CURRENT (mA)

0.08

0.04

0

-40.0 125.0

ALL PORTS LED (OFF)

TEMPERATURE (°C)

LED DRIVER SINK CURRENT

26

24

22

20

18

16

14

12

PORT SINK CURRENT (mA)

10

8

6

2.0 5.5

ALL PORTS
OUTPUT (0)

vs. V+

LED DROP = 2.4V

LED DROP = 1.8V

V+ (V)

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

8

MAX6956 toc01

97.570.042.515.0-12.5

7

V+ = 3.3V

6

5

SUPPLY CURRENT (µA)

4

3

-40.0 125.0

V+ = 5.5V

V+ = 2.5V

TEMPERATURE (°C)

MAX6956 toc02

97.570.042.515.0-12.5

LED DRIVER SINK CURRENT

vs. TEMPERATURE

27

V

= 2.4V

LED

26

MAX6956 toc04

25

24

23

22

PORT SINK CURRENT (mA)

21

20

5.04.53.5 4.03.02.5

-40.0 125.0
TEMPERATURE (°C)

V+ = 5.5V

V+ = 3.3V

MAX6956 toc05

97.570.042.515.0-12.5

OPERATING SUPPLY CURRENT vs. V+

(NO LOADS)

100

ALL PORTS LED (ON)

10

ALL PORTS OUTPUT (1)

1

SUPPLY CURRENT (mA)

0.1

0.01

2.0 5.5

ALL PORTS OUTPUT (0)

ALL PORTS LED (OFF)

V+ (V)

GPO SINK CURRENT vs. TEMPERATURE

(OUTPUT = 0)

18

V+ = 2.5V TO 5.5V, V

16

14

12

10

8

PORT SINK CURRENT (mA)

6

4

2

-40.0 125.0

= 0.6V

PORT

TEMPERATURE (°C)

MAX6956 toc03

5.04.54.03.53.02.5

MAX6956 toc06

97.570.0-12.5 15.0 42.5

GPO SOURCE CURRENT vs. TEMPERATURE

(OUTPUT = 1)

9

V

= 1.4V

PORT

8

7

6

5

4

PORT SOURCE CURRENT (mA)

3

2

-40.0 125.0

V+ = 5.5V

V+ = 3.3V

V+ = 2.5V

TEMPERATURE (°C)

1000

MAX6956 toc07

100

PULLUP CURRENT (µA)

97.570.042.515.0-12.5

10

-40.0 125.0

GPI PULLUP CURRENT

vs. TEMPERATURE

V+ = 5.5V

V+ = 3.3V

V+ = 2.5V

TEMPERATURE (°C)

GPO SHORT-CIRCUIT CURRENT

vs. TEMPERATURE

100

MAX6956 toc08

10

PORT CURRENT (mA)

GPO = 1, PORT

SHORTED TO GND

97.570.042.515.0-12.5

1

-40.0 125.0
TEMPERATURE (°C)

GPO = 0, PORT

SHORTED TO V+

MAX6956 toc09

97.570.042.515.0-12.5

Detailed Description

The MAX6956 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an I2C-com­patible serial interface. The ports can be configured to
any combination of constant-current LED drivers, logic
inputs and logic outputs, and default to logic inputs on
power-up. When fully configured as an LED driver, the
MAX6956 controls up to 28 LED segments with individ­ual 16-step adjustment of the constant current through
each LED segment. A single resistor sets the maximum
segment current for all segments, with a maximum of
24mA per segment. The MAX6956 drives any combina­tion of discrete LEDs and CA digits, including seven­segment and starburst alphanumeric types.

Figure 1 is the MAX6956 functional diagram. Any I/O
port can be configured as a push-pull output (sinking
10mA, sourcing 4.5mA), or a Schmitt-trigger logic
input. Each input has an individually selectable internal
pullup resistor. Additionally, transition detection allows
seven ports (P24 through P30) to be monitored in any
maskable combination for changes in their logic status.
A detected transition is flagged through a status regis­ter bit, as well as an interrupt pin (port P31), if desired.

The Typical Operating Circuit shows two MAX6956s
working together controlling three monocolor 16-seg-

ment-plus-DP displays, with five ports left available for
GPIO (P26–P31 of U2).

The port configuration registers set the 28 ports, P4 to
P31, individually as either LED drivers or GPIO. A pair
of bits in registers 0x09 through 0x0F sets each port’s
configuration (Tables 1 and 2).

The 36-pin MAX6956AAX has 28 ports, P4 to P31. The
28-pin MAX6956ANI and MAX6956AAI make only 20
ports available, P12 to P31. The eight unused ports
should be configured as outputs on power-up by writ­ing 0x55 to registers 0x09 and 0x0A. If this is not done,
the eight unused ports remain as floating inputs and
quiescent supply current rises, although there is no
damage to the part.

Register Control of I/O Ports and LEDs

Across Multiple Drivers

The MAX6956 offers 20 or 28 I/O ports, depending on
package choice. These can be applied to a variety of
combinations of different display types, for example:
seven, 7-segment digits (Figure 7). This example
requires two MAX6956s, with one digit being driven by
both devices, half by one MAX6956, half by the other
(digit 4 in this example). The two drivers are static, and
therefore do not need to be synchronized. The
MAX6956 sees CA digits as multiple discrete LEDs. To

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

_______________________________________________________________________________________ 5

Pin Description

PIN

SSOP/DI

1 1 36 ISET

2, 3 2, 3 37, 38, 39 GND Ground

4 4 40 AD0

5–24 ——P 12–P 31

— 5–32

——11, 20, 31 N.C. No Connection

25 33 32 SDA I2C-Compatible Serial Data I/O

26 34 33 SCL I2C-Compatible Serial Clock Input

27 35 34 AD1

28 36 35 V+ Positive Supply Voltage. Bypass V+ to GND with minimum 0.047µF capacitor.

SSOP T H I N Q F N

1–10, 12–19,

21–30

NAME FUNCTION

Segment Current Setting. Connect ISET to GND through a resistor (R
set the maximum segment current.

Address Input 0. Sets device slave address. Connect to either GND, V+, SCL,
SDA to give four logic combinations. See Table 3.

LED Segment Drivers and GPIO. P12 to P31 can be configured as CA LED
drivers, GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak
pullup resistor.

LED Segment Drivers and GPIO. P4 to P31 can be configured as CA LED

P4–P31

drivers, GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak
pullup resistor.

Address Input 1. Sets device slave address. Connect to either GND, V+, SCL,
SDA to give four logic combinations. See Table 3.

ISET

) to

MAX6956

simplify access to displays that overlap two MAX6956s,
the MAX6956 provides four virtual ports, P0 through P3.
To update an overlapping digit, send the same code
twice as an eight-port write, once to P28 through P35 of
the first driver, and again to P0 through P7 of the sec­ond driver. The first driver ignores the last 4 bits and
the second driver ignores the first 4 bits.

Two addressing methods are available. Any single port
(bit) can be written (set/cleared) at once; or, any
sequence of eight ports can be written (set/cleared) in
any combination at once. There are no boundaries; it is
equally acceptable to write P0 through P7, P1 through
P8, or P31 through P38 (P32 through P38 are nonexis­tent, so the instructions to these bits are ignored).

Using 8-bit control, a seven-segment digit with a deci­mal point can be updated in a single byte-write, a 14-

segment digit with DP can be updated in two byte­writes, and 16-segment digits with DP can be updated
in two byte-writes plus a bit write. Also, discrete LEDs
and GPIO port bits can be lit and controlled individually
without affecting other ports.

Shutdown

When the MAX6956 is in shutdown mode, all ports are
forced to inputs (which an be read), and the pullup cur­rent sources are turned off. Data in the port and control
registers remain unaltered, so port configuration and
output levels are restored when the MAX6956 is taken
out of shutdown. The display driver can still be pro­grammed while in shutdown mode. For minimum sup­ply current in shutdown mode, logic inputs should be at
GND or V+ potential. Shutdown mode is exited by set­ting the S bit in the configuration register (Table 8).

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

6 _______________________________________________________________________________________

Table 1. Port Configuration Map

Table 2. Port Configuration Matrix

Note: The logic is inverted between the two output modes; a high makes the output go low in LED segment driver mode (0x00) to
turn that segment on; in GPIO output mode (0x01), a high makes the output go high.

(

)

(

)

REGISTER

Port Configuration for P7, P6, P5, P4 0x09 P7 P6 P5 P4

Port Configuration for P11, P10, P9, P8 0x0A P11 P10 P9 P8

Port Configuration for P15, P14, P13, P12 0x0B P15 P14 P13 P12

Port Configuration for P19, P18, P17, P16 0x0C P19 P18 P17 P16

Port Configuration for P23, P22, P21, P20 0x0D P23 P22 P21 P20

Port Configuration for P27, P26, P25, P24 0x0E P27 P26 P25 P24

Port Configuration for P31, P30, P29, P28 0x0F P31 P30 P29 P28

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

REGISTER DATA

MODE FUNCTION

Output LED Segment Driver

Output GPIO Output

Input

Input GPIO Input with Pullup

GPIO Input

Without Pullup

PORT

REGISTER

0x20–0x5F

Register bit = 0 High impedance

Open-drain current sink, with sink

Register bit = 1

Register bit = 0 Active-low logic output

Register bit = 1 Active-high logic output

Register bit =

input logic level

current (up to 24mA) determined
by the appropriate current register

Schmitt logic input 0x09 to 0x0F 1 0

Schmitt logic input with pullup 0x09 to 0x0F 1 1

PIN BEHAVIOR

ADDRESS

CODE

HEX

0x09 to 0x0F 0 0

0x09 to 0x0F 0 1

CONFIGURATION

UPPER LOWER

PORT

BIT PAIR

Shutdown mode is temporarily overridden by the dis­play test function.

Serial Interface

Serial Addressing

The MAX6956 operates as a slave that sends and
receives data through an I2C-compatible 2-wire inter­face. The interface uses a serial data line (SDA) and a
serial clock line (SCL) to achieve bidirectional commu­nication between master(s) and slave(s). A master (typ­ically a microcontroller) initiates all data transfers to and
from the MAX6956, and generates the SCL clock that
synchronizes the data transfer (Figure 2).

The MAX6956 SDA line operates as both an input and
an open-drain output. A pullup resistor, typically 4.7kΩ,

is required on SDA. The MAX6956 SCL line operates
only as an input. A pullup resistor, typically 4.7kΩ, is
required on SCL if there are multiple masters on the 2­wire interface, or if the master in a single-master system
has an open-drain SCL output.

Each transmission consists of a START condition
(Figure 3) sent by a master, followed by the MAX6956
7-bit slave address plus R/W bit (Figure 6), a register
address byte, one or more data bytes, and finally a
STOP condition (Figure 3).

Start and Stop Conditions

Both SCL and SDA remain high when the interface is
not busy. A master signals the beginning of a transmis­sion with a START (S) condition by transitioning SDA
from high to low while SCL is high. When the master

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

_______________________________________________________________________________________________________ 7

Figure 1. MAX6956 Functional Diagram

INTENSITY REGISTERS

TEST REGISTER

PORT REGISTERS

MASK REGISTER

CONFIGURATION

REGISTERS

R/W

CEDATA

8

MAX6956

P4 TO P31

LED DRIVERS

OR GPIO

LED DRIVERS AND GPIO

SEGMENT OR

GPIO DATA

8

INTENSITY

TEST

CONFIGURATION

R/W

PORT CHANGE

DETECTOR

AD0

AD1

SDA

SCL

ADDRESS
MATCHER

7

D0 D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15

7

SLAVE ADDRESS BYTE

8

DATA BYTE COMMAND BYTE

R/W7-BIT DEVICE ADDRESS

COMMAND

REGISTER DECODE

8

TO/FROM DATA REGISTERS

TO COMMAND REGISTERS

COMMAND BYTEDATA BYTE

MAX6956

has finished communicating with the slave, it issues a
STOP (P) condition by transitioning SDA from low to
high while SCL is high. The bus is then free for another
transmission (Figure 3).

Bit Transfer

One data bit is transferred during each clock pulse.
The data on SDA must remain stable while SCL is high
(Figure 4).

Acknowledge

The acknowledge bit is a clocked 9th bit, which the
recipient uses to handshake receipt of each byte of
data (Figure 5). Thus, each byte transferred effectively
requires 9 bits. The master generates the 9th clock
pulse, and the recipient pulls down SDA during the
acknowledge clock pulse, such that the SDA line is sta­ble low during the high period of the clock pulse. When
the master is transmitting to the MAX6956, the
MAX6956 generates the acknowledge bit because the

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

8 _______________________________________________________________________________________

Figure 2. 2-Wire Serial Interface Timing Details

Figure 3. Standard Stop Conditions

Figure 4. Bit Transfer

SDA

t

BUF

SCL

t

SU, DAT

t

LOW

t

HD, DAT

t

SU, STA

t

HD, STA

t

SU, STO

t

HD, STA

START CONDITION

t

HIGH

t

R

SDA

SCL

S

START

CONDITION

SDA

t

F

REPEATED START CONDITION

P

STOP

CONDITION

START CONDITIONSTOP CONDITION

SCL

DATA LINE STABLE;

DATA VALID

CHANGE OF DATA ALLOWED

MAX6956 is the recipient. When the MAX6956 is trans­mitting to the master, the master generates the
acknowledge bit because the master is the recipient.

Slave Address

The MAX6956 has a 7-bit-long slave address (Figure 6).
The eighth bit following the 7-bit slave address is the
R/W bit. It is low for a write command, high for a read
command.

The first 3 bits (MSBs) of the MAX6956 slave address
are always 100. Slave address bits A3, A2, A1, and A0
are selected by address inputs, AD1 and AD0. These
two input pins may be connected to GND, V+, SDA, or
SCL. The MAX6956 has 16 possible slave addresses
(Table 3) and therefore, a maximum of 16 MAX6956
devices may share the same interface.

Message Format for Writing

the MAX6956

A write to the MAX6956 comprises the transmission of
the MAX6956’s slave address with the R/ W bit set to
zero, followed by at least 1 byte of information. The first

byte of information is the command byte. The com­mand byte determines which register of the MAX6956
is to be written by the next byte, if received. If a STOP
condition is detected after the command byte is
received, then the MAX6956 takes no further action
(Figure 8) beyond storing the command byte.

Any bytes received after the command byte are data
bytes. The first data byte goes into the internal register of
the MAX6956 selected by the command byte (Figure 9). If
multiple data bytes are transmitted before a STOP condi­tion is detected, these bytes are generally stored in subse­quent MAX6956 internal registers because the command
byte address generally autoincrements (Table 4).

Message Format for Reading

The MAX6956 is read using the MAX6956’s internally
stored command byte as address pointer, the same
way the stored command byte is used as address
pointer for a write. The pointer generally autoincre­ments after each data byte is read using the same rules
as for a write (Table 4). Thus, a read is initiated by first
configuring the MAX6956’s command byte by perform-

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

_______________________________________________________________________________________ 9

Figure 5. Acknowledge

Figure 6. Slave Address

START CONDITION

SCL

BY TRANSMITTER

SDA

SCL

SDA

S

SDA

BY RECEIVER

1 0 A3 A2 A1 A00

MSB

CLOCK PULSE FOR ACKNOWLEDGMENT

12 89

R/W

LSB

ACK

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

10 ______________________________________________________________________________________

Figure 7. Two MAX6956s Controlling Seven 7-Segment Displays

Figure 8. Command Byte Received

Figure 9. Command and Single Data Byte Received

7-SEGMENT DIGIT 1

7-SEGMENT DIGIT 2 7-SEGMENT DIGIT 3 7-SEGMENT DIGIT 4

VIRTUAL SEGMENTS

P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31

7-SEGMENT DIGIT 5 7-SEGMENT DIGIT 6 7-SEGMENT DIGIT 7

VIRTUAL SEGMENTS

P0 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31

V+

V+

COMMAND BYTE IS STORED ON RECEIPT OF STOP CONDITION

ACKNOWLEDGE FROM MAX6956

SAAP0

COMMAND BYTE RECEIVED

SLAVE ADDRESS

R/W

D15 D14 D13 D12 D11 D10 D9 D8

COMMAND BYTE

ACKNOWLEDGE FROM MAX6956

ACKNOWLEDGE FROM MAX6956 ACKNOWLEDGE FROM MAX6956

HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER

SAAAP0

ACKNOWLEDGE FROM MAX6956

SLAVE ADDRESS

R/W

D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6

COMMAND BYTE

DATA BYTE

1 BYTE

ing a write (Figure 8). The master can now read n con­secutive bytes from the MAX6956, with the first data
byte being read from the register addressed by the ini­tialized command byte. When performing read-after­write verification, remember to reset the command
byte’s address because the stored control byte
address generally has been autoincremented after the
write (Table 4). Table 5 is the register address map.

Operation with Multiple Masters

If the MAX6956 is operated on a 2-wire interface with
multiple masters, a master reading the MAX6956
should use a repeated start between the write, which
sets the MAX6956’s address pointer, and the read(s)
that takes the data from the location(s). This is because
it is possible for master 2 to take over the bus after
master 1 has set up the MAX6956’s address pointer but
before master 1 has read the data. If master 2 subse-

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 11

Figure 10. n Data Bytes Received

Table 3. MAX6956 Address Map

Table 4. Autoincrement Rules

HOW COMMAND BYTE AND DATA BYTE MAP INTO MAX6956's REGISTER

ACKNOWLEDGE FROM MAX6956

SA AAP0

AD1 AD0 A6 A5 A4 A3 A2 A1 A0

GND GND 1 0 0 0 0 0 0

GND V+ 1000001

GND SDA 1000010

GND SCL 1000011

V+ GND 1000100

V+ V+ 1000101

V+ SDA 1000110

V+ SCL 1000111

SDA GND 1001000

SDA V+ 1001001

SDA SDA 1 0 0 1 0 1 0

SDA SCL 1 0 0 1 0 1 1

SCL GND 1001100

SCL V+ 1001101

SCL SDA 1 0 0 1 1 1 0

SCL SCL 1 0 0 1 1 1 1

PIN

CONNECTION

SLAVE ADDRESS

R/W

ACKNOWLEDGE FROM MAX6956

D15 D14 D13 D12 D11 D10 D9 D8 D1 D0D3 D2D5 D4D7 D6

COMMAND BYTE

AUTOINCREMENT MEMORY WORD ADDRESS

DEVICE ADDRESS

ACKNOWLEDGE FROM MAX6956

DATA BYTE

n BYTES

COMMAND BYTE ADDRESS RANGE AUTOINCREMENT BEHAVIOR

x0000000 to x1111110 Command address autoincrements after byte read or written

x1111111 Command address remains at x1111111 after byte written or read

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

12 ______________________________________________________________________________________

Table 5. Register Address Map

REGISTER

No-Op X 0 0 0 0 0 0 0 0x00

Global Current X 0 0 0 0 0 1 0 0x02

Configuration X 0 0 0 0 1 0 0 0x04

Transition Detect Mask X 0 0 0 0 1 1 0 0x06

Display Test X 0 0 0 0 1 1 1 0x07

Port Configuration P7, P6, P5, P4 X 0 0 0 1 0 0 1 0x09

Port Configuration P11, P10, P9, P8 X 0 0 0 1 0 1 0 0x0A

Port Configuration P15, P14, P13, P12 X 0 0 0 1 0 1 1 0x0B

Port Configuration P19, P18, P17, P16 X 0 0 0 1 1 0 0 0x0C

Port Configuration P23, P22, P21, P20 X 0 0 0 1 1 0 1 0x0D

Port Configuration P27, P26, P25, P24 X 0 0 0 1 1 1 0 0x0E

Port Configuration P31, P30, P29, P28 X 0 0 0 1 1 1 1 0x0F

Current054

Current076

Current098 X 0 0 1 0 1 0 0 0x14

Current0BA X 0 0 1 0 1 0 1 0x15

Current0DC X 0 0 1 0 1 1 0 0x16

Current0FE X 0 0 1 0 1 1 1 0x17

Current110 X 0 0 1 1 0 0 0 0x18

Current132 X 0 0 1 1 0 0 1 0x19

Current154 X 0 0 1 1 0 1 0 0x1A

Current176 X 0 0 1 1 0 1 1 0x1B

Current198 X 0 0 1 1 1 0 0 0x1C

Current1BA X 0 0 1 1 1 0 1 0x1D

Current1DC X 0 0 1 1 1 1 0 0x1E

Current1FE X 0 0 1 1 1 1 1 0x1F

Port 0 only (virtual port, no action) X 0 1 0 0 0 0 0 0x20

Port 1 only (virtual port, no action) X 0 1 0 0 0 0 1 0x21

Port 2 only (virtual port, no action) X 0 1 0 0 0 1 0 0x22

Port 3 only (virtual port, no action) X 0 1 0 0 0 1 1 0x23

Port 4 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 0 0 0x24

Port 5 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 0 1 0x25

Port 6 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 1 0 0x26

Port 7 only (data bit D0; D7–D1 read as 0) X 0 1 0 0 1 1 1 0x27

Port 8 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 0 0 0x28

Port 9 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 0 1 0x29

Port 10 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 1 0 0x2A

D15 D14 D13 D12 D11 D10 D9 D8

X 0 0 1 0 0 1 0 0x12

X 0 0 1 0 0 1 1 0x13

COMMAND ADDRESS

HEX

CODE

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 13

Table 5. Register Address Map (continued)

REGISTER

Port 11 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 0 1 1 0x2B

Port 12 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 0 0 0x2C

Port 13 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 0 1 0x2D

Port 14 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 1 0 0x2E

Port 15 only (data bit D0; D7–D1 read as 0) X 0 1 0 1 1 1 1 0x2F

Port 16 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 0 0 0x30

Port 17 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 0 1 0x31

Port 18 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 1 0 0x32

Port 19 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 0 1 1 0x33

Port 20 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 0 0 0x34

Port 21 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 0 1 0x35

Port 22 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 1 0 0x36

Port 23 only (data bit D0; D7–D1 read as 0) X 0 1 1 0 1 1 1 0x37

Port 24 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 0 0 0x38

Port 25 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 0 1 0x39

Port 26 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 1 0 0x3A

Port 27 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 0 1 1 0x3B

Port 28 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 0 0 0x3C

Port 29 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 0 1 0x3D

Port 30 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 1 0 0x3E

Port 31 only (data bit D0; D7–D1 read as 0) X 0 1 1 1 1 1 1 0x3F

4 ports 4–7 (data bits D0–D3; D4–D7 read as 0) X 1 0 0 0 0 0 0 0x40

5 ports 4–8 (data bits D0–D4; D5–D7 read as 0) X 1 0 0 0 0 0 1 0x41

6 ports 4–9 (data bits D0–D5; D6–D7 read as 0) X 1 0 0 0 0 1 0 0x42

7 ports 4–10 (data bits D0–D6; D7 reads as 0) X 1 0 0 0 0 1 1 0x43

8 ports 4–11 (data bits D0–D7) X 1 0 0 0 1 0 0 0x44

8 ports 5–12 (data bits D0–D7) X 1 0 0 0 1 0 1 0x45

8 ports 6–13 (data bits D0–D7) X 1 0 0 0 1 1 0 0x46

8 ports 7–14 (data bits D0–D7) X 1 0 0 0 1 1 1 0x47

8 ports 8–15 (data bits D0–D7) X 1 0 0 1 0 0 0 0x48

8 ports 9–16 (data bits D0–D7) X 1 0 0 1 0 0 1 0x49

8 ports 10–17 (data bits D0–D7) X 1 0 0 1 0 1 0 0x4A

8 ports 11–18 (data bits D0–D7) X 1 0 0 1 0 1 1 0x4B

8 ports 12–19 (data bits D0–D7) X 1 0 0 1 1 0 0 0x4C

8 ports 13–20 (data bits D0–D7) X 1 0 0 1 1 0 1 0x4D

8 ports 14–21 (data bits D0–D7) X 1 0 0 1 1 1 0 0x4E

8 ports 15–22 (data bits D0–D7) X 1 0 0 1 1 1 1 0x4F

D15 D14 D13 D12 D11 D10 D9 D8

COMMAND ADDRESS

HEX

CODE

MAX6956

quently changes, the MAX6956’s address pointer, then
master 1’s delayed read may be from an unexpected
location.

Command Address Autoincrementing

Address autoincrementing allows the MAX6956 to be
configured with the shortest number of transmissions
by minimizing the number of times the command
address needs to be sent. The command address
stored in the MAX6956 generally increments after each
data byte is written or read (Table 4).

Initial Power-Up

On initial power-up, all control registers are reset, the
current registers are set to minimum value, and the
MAX6956 enters shutdown mode (Table 6).

LED Current Control

LED segment drive current can be set either globally or
individually. Global control simplifies the operation
when all LEDs are set to the same current level,
because writing just the global current register sets the
current for all ports configured as LED segment drivers.
It is also possible to individually control the current

drive of each LED segment driver. Individual/global
brightness control is selected by setting the configura­tion register I bit (Table 9). The global current register
(0x02) data are then ignored, and segment currents are
set using register addresses 0x12 through 0x1F (Tables
12, 13, and 14). Each segment is controlled by a nibble
of one of the 16 current registers.

Transition (Port Data Change) Detection

Port transition detection allows any combination of the
seven ports P24–P30 to be continuously monitored for
changes in their logic status (Figure 11). A detected
change is flagged on the transition detection mask reg­ister INT status bit, D7 (Table 15). If port P31 is config­ured as an output (Tables 1 and 2), then P31 also
automatically becomes an active-high interrupt output
(INT), which follows the condition of the INT status bit.
Port P31 is set as output by writing bit D7 = 0 and bit
D6 = 1 to the port configuration register (Table 1). Note
that the MAX6956 does not identify which specific
port(s) caused the interrupt, but provides an alert that
one or more port levels have changed.

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

14 ______________________________________________________________________________________

Table 5. Register Address Map (continued)

Note: Unused bits read as 0.

REGISTER

8 ports 16–23 (data bits D0–D7) X 1 0 1 0 0 0 0 0x50

8 ports 17–24 (data bits D0–D7) X 1 0 1 0 0 0 1 0x51

8 ports 18–25 (data bits D0–D7) X 1 0 1 0 0 1 0 0x52

8 ports 19–26 (data bits D0–D7) X 1 0 1 0 0 1 1 0x53

8 ports 20–27 (data bits D0–D7) X 1 0 1 0 1 0 0 0x54

8 ports 21–28 (data bits D0–D7) X 1 0 1 0 1 0 1 0x55

8 ports 22–29 (data bits D0–D7) X 1 0 1 0 1 1 0 0x56

8 ports 23–30 (data bits D0–D7) X 1 0 1 0 1 1 1 0x57

8 ports 24–31 (data bits D0–D7) X 1 0 1 1 0 0 0 0x58

7 ports 25–31 (data bits D0–D6; D7 reads as 0) X 1 0 1 1 0 0 1 0x59

6 ports 26–31 (data bits D0–D5; D6–D7 read as 0) X 1 0 1 1 0 1 0 0x5A

5 ports 27–31 (data bits D0–D4; D5–D7 read as 0) X 1 0 1 1 0 1 1 0x5B

4 ports 28–31 (data bits D0–D3; D4–D7 read as 0) X 1 0 1 1 1 0 0 0x5C

3 ports 29–31 (data bits D0–D2; D3–D7 read as 0) X 1 0 1 1 1 0 1 0x5D

2 ports 30–31 (data bits D0–D1; D2–D7 read as 0) X 1 0 1 1 1 1 0 0x5E

1 port 31 only (data bit D0; D1–D7 read as 0) X 1 0 1 1 1 1 1 0x5F

D15 D14 D13 D12 D11 D10 D9 D8

COMMAND ADDRESS

HEX

CODE

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

Table 6. Power-Up Configuration

X = unused bits; if read, zero results.

______________________________________________________________________________________ 15

REGISTER
FUNCTION

Port Register
Bits 4 to 31

Global
Current

Configuration
Register

Input Mask
Register

Display Test Normal Operation 0x07 X X X X X X X 0

Port
Configuration

Port
Configuration

Port
Configuration

Port
Configuration

Port
Configuration

Port
Configuration

Port
Configuration

Current054 1/16 (minimum on) 0x12 0 0 0 0 0 0 0 0

Current076 1/16 (minimum on) 0x13 0 0 0 0 0 0 0 0

Current098 1/16 (minimum on) 0x14 0 0 0 0 0 0 0 0

Current0BA 1/16 (minimum on) 0x15 0 0 0 0 0 0 0 0

Current0DC 1/16 (minimum on) 0x16 0 0 0 0 0 0 0 0

Current0FE 1/16 (minimum on) 0x17 0 0 0 0 0 0 0 0

Current110 1/16 (minimum on) 0x18 0 0 0 0 0 0 0 0

Current132 1/16 (minimum on) 0x19 0 0 0 0 0 0 0 0

Current154 1/16 (minimum on) 0x1A 0 0 0 0 0 0 0 0

Current176 1/16 (minimum on) 0x1B 0 0 0 0 0 0 0 0

Current198 1/16 (minimum on) 0x1C 0 0 0 0 0 0 0 0

Current1BA 1/16 (minimum on) 0x1D 0 0 0 0 0 0 0 0

Current1DC 1/16 (minimum on) 0x1E 0 0 0 0 0 0 0 0

Current1FE 1/16 (minimum on) 0x1F 0 0 0 0 0 0 0 0

P7, P6, P5, P4: GPIO Inputs Without Pullup 0x09 1 0 1 0 1 0 1 0

P11, P10, P9, P8: GPIO Inputs Without Pullup 0x0A 1 0 1 0 1 0 1 0

P15, P14, P13, P12: GPIO Inputs Without Pullup 0x0B 1 0 1 0 1 0 1 0

P19, P18, P17, P16: GPIO Inputs Without Pullup 0x0C 1 0 1 0 1 0 1 0

P23, P22, P21, P20: GPIO Inputs Without Pullup 0x0D 1 0 1 0 1 0 1 0

P27, P26, P25, P24: GPIO Inputs Without Pullup 0x0E 1 0 1 0 1 0 1 0

P31, P30, P29, P28: GPIO Inputs Without Pullup 0x0F 1 0 1 0 1 0 1 0

POWER-UP CONDITION

LED Off; GPIO Output Low

1/16 (minimum on) 0x02 X X X X 0 0 0 0

Shutdown Enabled

Current Control = Global

Transition Detection Disabled

All Clear (Masked Off) 0x06 X 0 0 0 0 0 0 0

ADDRESS

CODE

(HEX)

0x24 to

0x3F

0x04 0 0 X X X X X 0

D7 D6 D5 D4 D3 D2 D1 D0

XXXXXXX0

REGISTER DATA

MAX6956

The mask register contains 7 mask bits, which select
which of the seven ports P24–P30 are to be monitored
(Table 15). Set the appropriate mask bit to enable that
port for transition detect. Clear the mask bit if transitions
on that port are to be ignored. Transition detection
works regardless of whether the port being monitored is
set to input or output, but generally, it is not particularly
useful to enable transition detection for outputs.

To use transition detection, first set up the mask register
and configure port P31 as an output, as described
above. Then enable transition detection by setting the

M bit in the configuration register (Table 10). Whenever
the configuration register is written with the M bit set,
the MAX6956 updates an internal 7-bit snapshot regis­ter, which holds the comparison copy of the logic states
of ports P24 through P30. The update action occurs
regardless of the previous state of the M bit, so that it is
not necessary to clear the M bit and then set it again to
update the snapshot register.

When the configuration register is written with the M bit
set, transition detection is enabled and remains
enabled until either the configuration register is written

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

16 ______________________________________________________________________________________

Table 7. Configuration Register Format

Table 8. Shutdown Control (S Data Bit D0) Format

Table 10. Transition Detection Control (M-Data Bit D7) Format

Table 9. Global Current Control (I Data Bit D6) Format

FUNCTION

Configuration Register 0x04 M I XXXXXS

FUNCTION

Shutdown 0x04 M I XXXXX0

Normal Operation 0x04 M I XXXXX1

FUNCTION

Global

Constant-current limits for all digits are

controlled by one setting in the Global Current

register, 0x02

Individual Segment

Constant-current limit for each digit is

individually controlled by the settings in the

Current054 through Current1FE registers

ADDRESS CODE

(HEX)

ADDRESS CODE

(HEX)

D7 D6 D5 D4 D3 D2 D1 D0

D7 D6 D5 D4 D3 D2 D1 D0

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

0x04 M 0 XXXXXS

0x04 M 1 XXXXXS

REGISTER DATA

REGISTER DATA

REGISTER DATA

FUNCTION

Disabled 0x04 0 I XXXXXS

Enabled 0x04 1 I XXXXXS

ADDRESS CODE

(HEX)

D7 D6 D5 D4 D3 D2 D1 D0

REGISTER DATA

with the M bit clear, or a transition is detected. The INT
status bit (transition detection mask register bit D7)
goes low. Port P31 (if enabled as INT output) also goes
low, if it was not already low.

Once transition detection is enabled, the MAX6956
continuously compares the snapshot register against
the changing states of P24 through P31. If a change on
any of the monitored ports is detected, even for a short
time (like a pulse), the INT status bit (transition detec­tion mask register bit D7) is set. Port P31 (if enabled as
INT output) also goes high. The INT output and INT sta­tus bit are not cleared if more changes occur or if the
data pattern returns to its original snapshot condition.
The only way to clear INT is to access (read or write)
the transition detection mask register (Table 15). So if
the transition detection mask register is read twice in
succession after a transition event, the first time reads
with bit D7 set (identifying the event), and the second
time reads with bit D7 clear.

Transition detection is a one-shot event. When INT has
been cleared after responding to a transition event,
transition detection is automatically disabled, even
though the M bit in the configuration register remains
set (unless cleared by the user). Reenable transition
detection by writing the configuration register with the

M bit set, to take a new snapshot of the seven ports
P24 to P30.

Display Test Register

Display test mode turns on all ports configured as LED
drivers by overriding, but not altering, all controls and
port registers, except the port configuration register
(Table 16). Only ports configured as LED drivers are
affected. Ports configured as GPIO push-pull outputs
do not change state. In display test mode, each port’s
current is temporarily set to 1/2 the maximum current
limit as controlled by R

ISET

.

Selecting External Component R

ISET

to Set Maximum Segment Current

The MAX6956 uses an external resistor R

ISET

to set the
maximum segment current. The recommended value,
39kΩ, sets the maximum current to 24mA, which makes
the segment current adjustable from 1.5mA to 24mA in

1.5mA steps.

To set a different segment current, use the formula:

R

ISET

= 936kΩ / I

SEG

where I

SEG

is the desired maximum segment current.

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 17

Table 11. Global Segment Current Register Format

X = Don’t care bit.

LED DRIVE

FRACTION

1/16 1.5 0x02 X X X X 0 0 0 0 0xX0

2/16 3 0x02 X X X X 0 0 0 1 0xX1

3/16 4.5 0x02 X X X X 0 0 1 0 0xX2

4/16 6 0x02 X X X X 0 0 1 1 0xX3

5/16 7.5 0x02 X X X X 0 1 0 0 0xX4

6/16 9 0x02 X X X X 0 1 0 1 0xX5

7/16 10.5 0x02 X X X X 0 1 1 0 0xX6

8/16 12 0x02 X X X X 0 1 1 1 0xX7

9/16 13.5 0x02 X X X X 1 0 0 0 0xX8

10/16 15 0x02 X X X X 1 0 0 1 0xX9

11/16 16.5 0x02 X X X X 1 0 1 0 0xXA

12/16 18 0x02 X X X X 1 0 1 1 0xXB

13/16 19.5 0x02 X X X X 1 1 0 0 0xXC

14/16 21 0x02 X X X X 1 1 0 1 0xXD

15/16 22.5 0x02 X X X X 1 1 1 0 0xXE

16/16 24 0x02 X X X X 1 1 1 1 0xXF

TYPICAL SEGMENT

CURRENT (mA)

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

18 ______________________________________________________________________________________

Table 12. Individual Segment Current Registers

Table 13. Even Individual Segment Current Format

REGISTER
FUNCTION

Current054 register 0x12 Segment 5 Segment 4

Current076 register 0x13 Segment 7 Segment 6

Current098 register 0x14 Segment 9 Segment 8

Current0BA register 0x15 Segment 11 Segment 10

Current0DC register 0x16 Segment 13 Segment 12

Current0FE register 0x17 Segment 15 Segment 14

Current110 register 0x18 Segment 17 Segment 16

Current132 register 0x19 Segment 19 Segment 18

Current154 register 0x1A Segment 21 Segment 20

Current176 register 0x1B Segment 23 Segment 22

Current198 register 0x1C Segment 25 Segment 24

Current1BA register 0x1D Segment 27 Segment 26

Current1DC register 0x1E Segment 29 Segment 28

Current1FE register 0x1F Segment 31 Segment 30

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

LED DRIVE

FRACTION

1/16 1.5 0x12 to 0x1F 0000 0xX0

2/16 3 0x12 to 0x1F 0001 0xX1

3/16 4.5 0x12 to 0x1F 0010 0xX2

4/16 6 0x12 to 0x1F 0011 0xX3

5/16 7.5 0x12 to 0x1F 0100 0xX4

6/16 9 0x12 to 0x1F 0101 0xX5

7/16 10.5 0x12 to 0x1F See Table 14. 0110 0xX6

8/16 12 0x12 to 0x1F 0111 0xX7

9/16 13.5 0x12 to 0x1F 1000 0xX8

10/16 15 0x12 to 0x1F 1001 0xX9

11/16 16.5 0x12 to 0x1F 1010 0xXA

12/16 18 0x12 to 0x1F 1011 0xXB

13/16 19.5 0x12 to 0x1F 1100 0xXC

14/16 21 0x12 to 0x1F 1101 0xXD

15/16 22.5 0x12 to 0x1F 1110 0xXE

16/16 24 0x12 to 0x1F 1111 0xXF

SEGMENT

CONSTANT

CURRENT WITH

R

= 39kΩ (mA)

ISET

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 19

The recommended value of R

ISET

is 39kΩ.

The recommended value of R

ISET

is the minimum
allowed value, since it sets the display driver to the
maximum allowed segment current. R

ISET

can be a
higher value to set the segment current to a lower maxi­mum value where desired. The user must also ensure
that the maximum current specifications of the LEDs
connected to the driver are not exceeded.

The drive current for each segment can be controlled
through programming either the Global Current register
(Table 11) or Individual Segment Current registers
(Tables 12, 13, and 14), according to the setting of the
Current Control bit of the Configuration register (Table 9).
These registers select the LED’s constant-current drive
from 16 equal fractions of the maximum segment cur­rent. The current difference between successive current
steps, I

STEP

, is therefore determined by the formula:

I

STEP

= I

SEG

/ 16

If I

SEG

= 24mA, then I

STEP

= 24mA / 16 = 1.5mA.

Applications Information

Driving Bicolor and Tricolor LEDs

Bicolor digits group a red and a green die together for
each display element, so that the element can be lit
red, green (or orange), depending on which die (or
both) is lit. The MAX6956 allows each segment’s cur­rent to be set individually from 1/16th (minimum current
and LED intensity) to 16/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 289
color/intensity combinations. A discrete or CA tricolor
(red-green-yellow or red-green-blue) segment triad can
be set to 4913 color/intensity combinations.

Power Dissipation Issues

Each MAX6956 port can sink a current of 24mA into an
LED with a 2.4V forward-voltage drop when operated
from a supply voltage of at least 3.0V. The minimum
voltage drop across the internal LED drivers is there­fore (3.0V - 2.4V) = 0.6V. The MAX6956 can sink 28 x
24mA = 672mA when all outputs are operating as LED

Table 14. Odd Individual Segment Current Format

LED

DRIVE

FRACTION

1/16 1.5 0x12 to 0x1F 0 0 0 0 0x0X

2/16 3 0x12 to 0x1F 0 0 0 1 0x1X

3/16 4.5 0x12 to 0x1F 0 0 1 0 0x2X

4/16 6 0x12 to 0x1F 0 0 1 1 0x3X

5/16 7.5 0x12 to 0x1F 0 1 0 0 0x4X

6/16 9 0x12 to 0x1F 0 1 0 1 0x5X

7/16 10.5 0x12 to 0x1F 0 1 1 0 See Table 13. 0x6X

8/16 12 0x12 to 0x1F 0 1 1 1 0x7X

9/16 13.5 0x12 to 0x1F 1 0 0 0 0x8X

10/16 15 0x12 to 0x1F 1 0 0 1 0x9X

11/16 16.5 0x12 to 0x1F 1 0 1 0 0xAX

12/16 18 0x12 to 0x1F 1 0 1 1 0xBX

13/16 19.5 0x12 to 0x1F 1 1 0 0 0xCX

14/16 21 0x12 to 0x1F 1 1 0 1 0xDX

15/16 22.5 0x12 to 0x1F 1 1 1 0 0xEX

16/16 24 0x12 to 0x1F 1 1 1 1 0xFX

SEGMENT

CONSTANT

CURRENT WITH

= 39kΩ (mA)

R

ISET

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0 HEX CODE

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

20 ______________________________________________________________________________________

Figure 11. Maskable GPIO Ports P24 Through P31

P31

P30

P29

P28

P27

GPIO INPUT

CONDITIONING

OUTPUT LATCH

OUTPUT LATCH

CONFIGURATION REGISTER M BIT = 1

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO/PORT

INT

GPIO/PORT OUT

GPIO/PORT OUT

GPIO/PORT OUT

GPIO/PORT OUT

GPIO IN

GPIO IN

GPIO IN

GPIO IN

GPIO IN

GPIO/PORT OUT

INT STATUS STORED AS MSB OF MASK REGISTER

R

S

CLOCK PULSE AFTER EACH READ ACCESS TO MASK REGISTER

D Q

MASK REGISTER BIT 6

D Q

MASK REGISTER BIT 5

D Q

MASK REGISTER BIT 4

D Q

MASK REGISTER BIT 3

OR

GPIO IN

GPIO/PORT OUT

GPIO IN

GPIO/PORT OUT

GPIO IN

GPIO/PORT OUT

D Q

MASK REGISTER BIT 2

D Q

MASK REGISTER BIT 1

D Q

MASK REGISTER LSB

CLOCK PULSE WHEN WRITING CONFIGURATION REGISTER WITH M BIT SET

P26

P25

P24

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

GPIO INPUT

CONDITIONING

GPIO/PORT OUTPUT LATCH

segment drivers at full current. On a 3.3V supply, a
MAX6956 dissipates (3.3V - 2.4V) ✕672mA = 0.6W
when driving 28 of these 2.4V forward-voltage drop
LEDs at full current. This dissipation is within the ratings
of the 36-pin SSOP package with an ambient tempera­ture up to +98°C. If a higher supply voltage is used or
the LEDs used have a lower forward-voltage drop than

2.4V, the MAX6956 absorbs a higher voltage, and the
MAX6956’s power dissipation increases.

If the application requires high drive current and high
supply voltage, consider adding a series resistor to
each LED to drop excessive drive voltage off-chip. For
example, consider the requirement that the MAX6956
must drive LEDs with a 2.0V to 2.4V specified forward­voltage drop, from an input supply range is 5V ±5%
with a maximum LED current of 20mA. Minimum input
supply voltage is 4.75V. Maximum LED series resistor
value is (4.75V - 2.4V - 0.6V)/0.020A = 87.5Ω. We
choose 82Ω ±2%. Worst-case resistor dissipation is at
maximum toleranced resistance, i.e., (0.020A)

2

✕

(82Ω

✕

1.02) = 34mW. The maximum MAX6956 dissipation
per LED is at maximum input supply voltage, minimum
toleranced resistance, minimum toleranced LED for­ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A

✕

82Ω x 0.98)) = 32.86mW. Worst-case MAX6956 dissi­pation is 920mW driving all 28 LEDs at 20mA full cur­rent at once, which meets the 941mW dissipation
ratings of the 36-pin SSOP package.

Low-Voltage Operation

The MAX6956 operates down to 2V supply voltage
(although the sourcing and sinking currents are not guar­anteed), providing that the MAX6956 is powered up ini­tially to at least 2.5V to trigger the device’s internal reset.

Serial Interface Latency

When a MAX6956 register is written through the I2C inter­face, the register is updated on the rising edge of SCL
during the data byte’s acknowledge bit (Figure 5). The
delay from the rising edge of SCL to the internal register
being updated can range from 50ns to 350ns.

PC Board Layout Considerations

Ensure that all of the MAX6956 GND connections are
used. A ground plane is not necessary, but may be useful
to reduce supply impedance if the MAX6956 outputs are
to be heavily loaded. Keep the track length from the ISET
pin to the R

ISET

resistor as short as possible, and take the
GND end of the resistor either to the ground plane or
directly to the GND pins.

Power-Supply Considerations

The MAX6956 operates with power-supply voltages of

2.5V to 5.5V. Bypass the power supply to GND with a

0.047µF capacitor as close to the device as possible.
Add a 1µF capacitor if the MAX6956 is far away from
the board’s input bulk decoupling capacitor.

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 21

Table 15. Transition Detection Mask Register

*INT is automatically cleared after it is read.

Table 16. Display Test Register

X = Don’t care bit

FUNCTION

Mask

Register

MODE

Normal Operation 0x07 XXXXXXX0

Display Test Mode 0x07 XXXXXXX1

REGISTER
ADDRESS

(HEX)

0x06

READ/

WRITE

Read INT Status*

Write Unchanged

ADDRESS CODE

(HEX)

REGISTER DATA

D7 D6 D5 D4 D3 D2 D1 D0

Port

30

mask

D7 D6 D5 D4 D3 D2 D1 D0

Port

29

mask

Port

28

mask

REGISTER DATA

Port

27

mask

Port

26

mask

Port

25

mask

Port

mask

24

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

22 ______________________________________________________________________________________

Typical Operating Circuit

3V

a1
a2

b
c
d1
d2
e

f
g1
g2
h
i

j
k
l
m
dp
ca

a1
a2

b
c
d1
d2
e

f
g1
g2
h
i

j
k
l
m
dp
ca

a1
a2

b
c
d1
d2
e

f
g1
g2
h
i

j
k
l
m
dp
ca

LED1

LED2

LED3

DATA

CLOCK

IRQ OUT

SW2SW1

47nF

47nF

SW3

3V

3V

212

39kΩ

39kΩ

36

V+

3

GND

2

GND

1

ISET

35

AD1

4

AD0

33

SDA

34

SCL

31

P31

29

P30

27

P29

25

P28

24

P27

23

P26

22

P25

21

P24

36

V+

3

GND

2

GND

1

ISET

35

AD1

4

AD0

33

SDA

34

SCL

31

P31

29

P30

27

P29

25

P28

24

P27

23

P26

22

P25

21

P24

U1

MAX6956AAX

U2

MAX6956AAX

P10

P11
P12
P13
P14
P15

P16
P17
P18
P19
P20

P21
P22
P23

P10

P11
P12
P13
P14
P15

P16
P17
P18
P19
P20

P21
P22
P23

32

P4

30

P5

28

P6

26

P7

5

P8

7

P9

9
11
6

8
10

12
13
14
15

16
17
18
19
20

32

P4

30

P5

28

P6

26

P7

5

P8

7

P9

9
11
6

8
10

12
13
14
15

16
17
18
19
20

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 23

Pin Configurations (continued)

Chip Information

TRANSISTOR COUNT: 33,559

PROCESS: CMOS

TOP VIEW

1

ISET

2

GND

3

GND

4

AD0

5

P8

6

P12

7

P9

8

P13

9

P10

10

P14

11

P11

12

P15

13

P16

P17

14

15

P18

16

P19

17

P20

18 P22

P21

MAX6956

36

V+

35

AD1

34

SCL

33

SDA

32

P4

31

P31

30

P5

P30

29

28

P6

27

P29

26

P7

25

P28

24

P27

23

P26

22

P25

21

P24

20

P23

19

P12

P13
P10

P14

P11
P15
P16

P17

1

P8

2

3

P9

4

5

6

7

8

9

10

GND

GND

GND

AD0

403938373635343332

ISETV+AD1

SCL

MAX6956

111213141516171819

P21

P22

N.C.

P18

P19

P20

P23

P24

QFN

SDA

P25

N.C.

31

20

N.C.

30

P4

29

P31

28

P5

27

P30
P6

26

P29

25

P7

24

P28

23

P27

22

P26

21

SSOP

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

24 ______________________________________________________________________________________

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

12

INCHES

DIM

MIN

A

0.068

A1

0.002

B

0.010

C

HE

N

D

E

e

H

L

0.004

SEE VARIATIONS

0.205

0.0256 BSC

0.301

0.025

0∞

MAX

0.078

0.008

0.015

0.008

0.212

0.311

0.037

8∞

MILLIMETERS

MAX

MIN

1.73 1.99

0.21

0.05

0.38

0.25

0.20

0.09

5.20

5.38

0.65 BSC

7.65

7.90

0.63

0.95

0∞

8∞

INCHES

MIN

D

0.239

D

0.239

D

0.278

D

0.317

0.397

D

MAX

0.249

0.249

0.289

0.328

0.407

MILLIMETERS

MAX

MIN

6.07

6.33

6.07

6.33

7.07

7.33

8.07

8.33

10.07

10.33

N

14L
16L

20L

24L

28L

SSOP.EPS

A

e

D

B

A1

L

NOTES:

1. D&E DO NOT INCLUDE MOLD FLASH.

2. MOLD FLASH OR PROTRUSIONS NOT TO EXCEED .15 MM (.006").

3. CONTROLLING DIMENSION: MILLIMETERS.

4. MEETS JEDEC MO150.

5. LEADS TO BE COPLANAR WITHIN 0.10 MM.

PROPRIETARY INFORMATION

TITLE:

PACKAGE OUTLINE, SSOP, 5.3 MM

21-0056

C

REV.DOCUMENT CONTROL NO.APPROVAL

1

C

1

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

______________________________________________________________________________________ 25

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

36

1

TOP VIEW

e

INCHES

DIM

MIN

0.096A

0.004

A1

0.012

B

0.009

C

HE

D

A1

A

B

C

e 0.0315 BSC 0.80 BSC

0.291

E
H 0.4140.398 10.11 10.51

0.020L

D 0.6120.598

L

MAX

0.104

0.011

0.017

0.013

0.299

0.040

MILLIMETERS

MAX

MIN

2.65

2.44

0.29

0.10

0.44

0.30

0.23

0.32

7.40 7.60

0.51 1.02

15.20 15.55

0∞-8∞

SSOP.EPS

FRONT VIEW

SIDE VIEW

PROPRIETARY INFORMATION

TITLE:

PACKAGE OUTLINE, 36L SSOP, 0.80 MM PITCH

REV.DOCUMENT CONTROL NO.APPROVAL

21-0040 E

1

1

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or
28-Port LED Display Driver and I/O Expander

26 ______________________________________________________________________________________

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

D

D/2

E/2

(NE-1) X e

A1 A2

E

A

k

D2

C

L

D2/2

e

(ND-1) X e

C

L

e e

PACKAGE OUTLINE
36,40L THIN QFN, 6x6x0.8 mm

21-0141

b

E2/2

C

E2

L

k

L

C

L

D

QFN THIN 6x6x0.8.EPS

LL

1

2

MAX6956

2-Wire-Interfaced, 2.5V to 5.5V, 20-Port or

28-Port LED Display Driver and I/O Expander

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 27

© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

NOTES:

1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.

2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.

3. N IS THE TOTAL NUMBER OF TERMINALS.

4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1
SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE
ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.

5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm
FROM TERMINAL TIP.

6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.

7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.

8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.

9. DRAWING CONFORMS TO JEDEC MO220.

10. WARPAGE SHALL NOT EXCEED 0.10 mm.

PACKAGE OUTLINE
36, 40L THIN QFN, 6x6x0.8 mm

21-0141

2

D

2