MAXIM MAX6954 Technical data

General Description

The MAX6954 is a compact display driver that inter­faces microprocessors to a mix of 7-segment, 14-seg­ment, and 16-segment LED displays through an SPI™­or QSPI™-compatible 4-wire serial interface. The serial
interface may be cascaded through multiple devices.
The MAX6954 drives up to 16 digits 7-segment, 8 digits
14-segment, 8 digits 16-segment, or 128 discrete
LEDs, while functioning from a supply voltage as low as

2.7V. The driver includes five I/O expander (or GPIO)
lines, some or all or which may be configured as a key­switch reader, which automatically scans and
debounces a matrix of up to 32 switches.

Included on chip are full 14- and 16-segment ASCII
104-character fonts, a hexadecimal font for 7-segment
displays, multiplex scan circuitry, anode and cathode
drivers, and static RAM that stores each digit. The max­imum segment current for the display digits is set using
a single external resistor. Digit intensity can be inde­pendently adjusted using the 16-step internal digital
brightness control. The MAX6954 includes a low-power
shutdown mode, a scan-limit register that allows the
user to display from 1 to 16 digits, segment blinking
(synchronized across multiple drivers, if desired), and a
test mode, which forces all LEDs on. The LED drivers
are slew-rate limited to reduce EMI.

For a 2-wire interfaced version, refer to the MAX6955
data sheet. An evaluation kit (EV kit) for the MAX6955 is
available.

Applications

Set-Top Boxes Automotive

Panel Meters Bar Graph Displays

White Goods Audio/Video Equipment

Features

♦ High-Speed 26MHz SPI/QSPI/MICROWIRE™-

Compatible Serial Interface

♦ 2.7V to 5.5V Operation

♦ Drives Up to 16 Digits 7-Segment, 8 Digits

14-Segment, 8 Digits 16-Segment, 128 Discrete
LEDs, or a Combination of Digit Types

♦ Drives Common-Cathode Monocolor and Bicolor

LED Displays

♦ Built-In ASCII 104-Character Font for 14-Segment

and 16-Segment Digits and Hexadecimal Font for
7-Segment Digits

♦ Automatic Blinking Control for each Segment

♦ 10µA (typ) Low-Power Shutdown (Data Retained)

♦ 16-Step Digit-by-Digit Digital Brightness Control

♦ Display Blanked on Power-Up

♦ Slew-Rate Limited Segment Drivers for Lower EMI

♦ Five GPIO Port Pins Can Be Configured as Key-

Switch Reader to Scan and Debounce Up to 32
Switches with n-Key Rollover

♦ IRQ Output when a Key Input Is Debounced

♦ 36-Pin SSOP and 40-Pin DIP Packages

♦ Automotive Temperature Range Standard

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

19-2460; Rev 2; 8/05

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.

PART

TEMP RANGE

PIN-

PKG CODE

MAX6954AAX

36 SSOP A36-2

MAX6954APL

40 PDIP P40-2

SPI and QSPI are trademarks of Motorola, Inc.

MICROWIRE is a trademark of National Semiconductor Corp.

Pin Configurations and Typical Operating Circuits appear
at end of data sheet.

ISET

OSC

OSC_OUT

BLINK

CLK

CS

DIN

DOUT

4-WIRE SERIAL INTERFACE

RAM

BLINK

CONTROL

CONFIGURATION

REGISTER

CHARACTER
GENERATOR

ROM

CURRENT

SOURCE

DIVIDER/
COUNTER
NETWORK

DIGIT

MULTIPLEXER

PWM

BRIGHTNESS

CONTROL

GPIO

AND KEY-SCAN

CONTROL

LED

DRIVERS

O0 TO O23

P0 TO P4

MAX6954

Functional Diagram

PACKAGE

-40°C to +125°C

-40°C to +125°C

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

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

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

Current

O0–O7 Sink Current ......................................................935mA

O0–O18 Source Current .................................................55mA

DIN, CLK,

CS, OSC, DOUT, BLINK, OSC_OUT, ISET ....20mA

P0, P1, P2, P3, P4 ...........................................................40mA

GND .....................................................................................1A

Continuous Power Dissipation (T

A

= +70°C)

36-Pin SSOP (derate at 11.8mW/°C above +70°C) .....941mW

40-Pin PDIP (derate at 16.7mW/°C above +70°C).....1333mW

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

DC ELECTRICAL CHARACTERISTICS

(Typical Operating Circuits, V+ = 2.7V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

Operating Supply Voltage V+ 2.7 5.5 V

TA = +25°C 10 35

Shutdown Supply Current I

SHDN

Shutdown mode, all
digital inputs at V+
or GND

T

A

= T

MIN

to T

MAX

40

µA

TA = +25°C 22 30

Operating Supply Current I+

All segments on, all
digits scanned,
intensity set to full,
internal oscillator,
DOUT open circuit,
no display or
OSC_OUT load
connected

T

A

= T

MIN

to T

MAX

35

mA

OSC = RC oscillator, R

SET

= 56kΩ,

C

SET

= 22pF, V+ = 3.3V

4

Master Clock Frequency f

OSC

OSC driven externally 1 8

MHz

Dead Clock Protection Frequency

f

OSC

95 kHz

OSC Internal/External Detection
Threshold

V

OSC

1.7 V

OSC High Time t

CH

50 ns

OSC Low Time t

CL

50 ns

Slow Segment Blink Period

OSC = RC oscillator, R

SET

= 56kΩ,

C

SET

= 22pF, V+ = 3.3V

1s

Fast Segment Blink Period

OSC = RC oscillator, R

SET

= 56kΩ,

C

SET

= 22pF, V+ = 3.3V

0.5 s

Fast or Slow Segment Blink Duty
Cycle

%

SYMBOL

MIN TYP MAX

f

SLOWBLINK

f

FASTBLINK

49.5 50.5

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

_______________________________________________________________________________________ 3

DC ELECTRICAL CHARACTERISTICS (continued)

(Typical Operating Circuits, V+ = 2.7V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

Segment Drive Source Current I

SEG

V

LED

= 2.2V,

V+

= 3.3V

T

A

= +25°C

-40

mA

Segment Current Slew Rate

TA = +25°C, V+ = 3.3V 11

mA/µs

Segment Drive Current Matching

∆I

SEGTA

= +25°C, V+ = 3.3V 5 10 %

LOGIC INPUTS AND OUTPUTS

Input Leakage Current
DIN, CLK, CS, OSC, P0, P1, P2,
P3, P4

I

IH

, I

IL

-1 +1 µA

4-Wire Logic-High Input Voltage
DIN, CLK, CS

V

IHSPI

1.8 V

4-Wire Logic-Low Input Voltage
DIN, CLK, CS

V

ILSPI

0.6 V

Port Logic-High Input Voltage
P0, P1, P2, P3, P4

V

IHP

0.7 x
V+

V

Port Logic-Low Input Voltage
P0, P1, P2, P3, P4

V

ILP

0.3 x
V+

V

Port Hysteresis Voltage P0, P1,
P2, P3, P4

∆V

IP

0.03 x
V+

V

Port Input Pullup Current from V+

I

IPU

P0 to P3 configured as keyscan input, V+ =

3.3V

75 µA

Port Output Low Voltage V

OLP

I

SINK

= 8mA 0.3 0.5 V

Blink Output Low Voltage V

OLBKISINK

= 0.6mA 0.1 0.3 V

DOUT Output High Voltage

I

SOURCE

= 1.6mA

V+ -

0.2

V

DOUT Output Low Voltage

I

SINK

= 1.6mA 0.2 V

OSC_OUT Output High Voltage

I

SOURCE

= 1.6mA

V+ -

0.4

V

OSC_OUT Output Low Voltage

I

SINK

= 1.6mA 0.4 V

SYMBOL

∆I

SEG

V

OHDO

V

OLDO

V

OHOSC

V

OLOSC

/∆t

MIN TYP MAX

-34.5

-46.5

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

4 _______________________________________________________________________________________

Typical Operating Characteristics

(V+ = 3.3V, LED forward voltage = 2.4V, typical application circuit, TA= +25°C, unless otherwise noted.)

TIMING CHARACTERISTICS

(Typical Operating Circuits, V+ = 2.7V to 5.5V, TA= T

MIN

to T

MAX

, unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

TIMING CHARACTERISTICS

CLK Clock Period t

CP

ns

CLK Pulse Width High t

CH

16 ns

CLK Pulse Width Low t

CL

16 ns

CS Fall to CLK Rise Setup Time t

CSS

9.5 ns

CLK Rise to CS Rise Hold Time t

CSH

0ns

DIN Setup Time t

DS

9.5 ns

DIN Hold Time t

DH

0ns

V+ = 3.0V to 5.5V 19

Output Data Propagation Delay t

DO

V+ = 2.7V 25

ns

DOUT Output Rise and Fall Times t

FT

C

LOAD

= 10pF, V+ = 3.0V to 5.5V 10

Minimum CS Pulse High t

CSW

ns

Note 1: All parameters tested at TA= +25°C. Specifications over temperature are guaranteed by design.

INTERNAL OSCILLATOR FREQUENCY

vs. TEMPERATURE

MAX6954 toc01

TEMPERATURE (°C)

OSCILLATOR FREQUENCY (MHz)

110805020-10

3.8

4.0

4.2

4.4

3.6

-40

R

SET

= 56kΩ

C

SET

= 22pF

INTERNAL OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

MAX6954 toc02

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY (MHz)

5.04.54.03.53.0

3.8

4.2

4.4

3.6

2.5 5.5

R

SET

= 56kΩ

C

SET

= 22pF

4.0

100ns/div

OSC: 500mV/div

OSC_OUT: 2V/div

MAX6954 toc03

OSC

0V

0V

OSC_OUT

INTERNAL OSCILLATOR WAVEFORM

AT OSC AND OSC_OUT PINS

R

SET

= 56k

Ω

C

SET

= 22pF

SYMBOL

MIN TYP MAX

38.4

19.5

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(V+ = 3.3V, LED forward voltage = 2.4V, typical application circuit, TA= +25°C, unless otherwise noted.)

DEAD CLOCK OSCILLATOR FREQUENCY

vs. SUPPLY VOLTAGE

MAX6954 toc04

SUPPLY VOLTAGE (V)

OSCILLATOR FREQUENCY (kHz)

5.04.54.03.53.0

85

95

105

110

80

2.5 5.5

R

SET

= 56k

Ω

OSC = GND

100

90

SEGMENT SOURCE CURRENT

vs. SUPPLY VOLTAGE

MAX6954 toc05

SUPPLY VOLTAGE (V)

CURRENT NORMALIZED TO 40mA

5.04.54.03.53.0

0.94

0.98

1.00

1.02

0.92

2.5 5.5

V

LED

= 1.8V

0.96

1V/div

200µs/div

MAX6954 toc06

O0

O18

WAVEFORM AT PINS O0 AND O18,

MAXIMUM INTENSITY

0V

0V

GPIO SINK CURRENT

vs. TEMPERATURE

MAX6954 toc07

TEMPERATURE (°C)

GPIO SINK CURRENT (mA)

11050 8020-10

5

10

15

20

25

30

35

40

45

0

-40

VCC = 3.3V

VCC = 2.5V

VCC = 5.5V

OUTPUT = LOW
V

PORT

= 0.6V

PORT INPUT PULLUP CURRENT

vs. TEMPERATURE

MAX6954 toc08

TEMPERATURE (°C)

KEY-SCAN SOURCE CURRENT (mA)

11050 8020-10

0.05

0.10

0.15

0.20

0.25

0.30

0

-40

VCC = 3.3V

VCC = 2.5V

VCC = 5.5V

OUTPUT = HIGH
V

PORT

= 1.4V

400µs/div

KEY_A: 1V/div

IRQ: 2V/div

MAX6954 toc09

KEY_A

0V

0V

IRQ

KEYSCAN OPERATION

(KEY_A AND IRQ)

MAX6954

Detailed Description

The MAX6954 is a serially interfaced display driver that
can drive up to 16 digits 7-segment, 8 digits 14-seg­ment, 8 digits 16-segment, 128 discrete LEDs, or a
combination of these display types. Table 1 shows the
drive capability of the MAX6954 for monocolor and
bicolor displays.

The MAX6954 includes 104-character ASCII font maps
for 14-segment and 16-segment displays, as well as
the hexadecimal font map for 7-segment displays. The
characters follow the standard ASCII font, with the
addition of the following common symbols: £, A€ , ¥, °, µ,
±, ↑, and ↓. Seven bits represent the 104-character font

map; an 8th bit is used to select whether the decimal
point (DP) is lit. Seven-segment LED digits may be con­trolled directly or use the hexadecimal font. Direct seg­ment control allows the MAX6954 to be used to drive
bar graphs and discrete LED indicators.

Tables 2, 3, and 4 list the connection schemes for 16-,
14-, and 7-segment digits, respectively. The letters in
Tables 2, 3, and 4 correspond to the segment labels
shown in Figure 1. (For applications that require mixed
display types, see Tables 37–40.)

Serial Interface

The MAX6954 communicates through an SPI-compati­ble 4-wire serial interface. The interface has three

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

6 _______________________________________________________________________________________

Pin Description

PIN

SSOP

PDIP

NAME FUNCTION

1, 2,

34, 35, 36

1, 2,

P0–P4

General-Purpose I/O Ports (GPIOs). GPIO can be configured as logic inputs or open-drain
outputs. Enabling key scanning configures some or all ports P0–P3 as key-switch matrix
inputs with internal pullup and port P4 as IRQ output.

33CS

Chip-Select Input. Serial data is loaded into the shift register while CS is low. The most recent
16 bits of data latch on CS’s rising edge.

44DOUT

Serial-Data Output. The data into DIN is valid at DOUT 15.5 clock cycles later. Use this pin to
daisy-chain several devices or allow data readback. Output is push-pull.

55CLK

Serial-Clock Input. On CLK’s rising edge, data shifts into the internal shift register. On CLK’s
falling edge, data is clocked out of DOUT. CLK is active only while CS is low.

66DIN

Serial-Data Input. Data from DIN loads into the internal 16-bit shift register on CLK’s rising
edge.

7–15,

22–31

7–15,

26–35

Digit/Segment Drivers. When acting as digit drivers, outputs O0 to O7 sink current from the
display common cathodes. When acting as segment drivers, O0 to O18 source current to the
display anodes. O0 to O18 are high impedance when not being used as digit or segment
drivers.

16, 18

GND Ground

17 19 ISET

Segment Current Setting. Connect ISET to GND through series resistor R

SET

to set the peak

current.

19, 21

V+

Positive Supply Voltage. Bypass V+ to GND with a 47µF bulk capacitor and a 0.1µF ceramic
capacitor.

20 22 OSC

Multiplex Clock Input. To use internal oscillator, connect capacitor C

SET

from OSC to GND.

To use external clock, drive OSC with a 1MHz to 8MHz CMOS clock.

32 36 BLINK Blink Clock Output. Output is open drain.

33 37

Clock Output. OSC_OUT is a buffered clock output to allow easy blink synchronization of
multiple MAX6954s. Output is push-pull.

— 16, 25 N.C. Not Connected Internally

38, 39, 40

O0–O18

17, 18, 20

21, 23, 24

OSC_OUT

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

_______________________________________________________________________________________ 7

inputs: clock (CLK), chip select (CS), and data in (DIN),
and one output, data out (DOUT). CS must be low to
clock data into or out of the device, and DIN must be
stable when sampled on the rising edge of CLK. DOUT
is stable on the rising edge of CLK. Note that while the
SPI protocol expects DOUT to be high impedance
when the MAX6954 is not being accessed, DOUT on
the MAX6954 is never high impedance.

CLK and DIN may be used to transmit data to other
peripherals. The MAX6954 ignores all activity on CLK
and DIN except when CS is low.

Control and Operation Using the 4-Wire Interface

Controlling the MAX6954 requires sending a 16-bit
word. The first byte, D15 through D8, is the command,
and the second byte, D7 through D0, is the data byte
(Table 5).

Connecting Multiple MAX6954s to the 4-Wire Bus

Multiple MAX6954s may be daisy-chained by connect­ing the DOUT of one device to the DIN of the next, and
driving CLK and CS lines in parallel (Figure 2). Data at
DIN propagates through the internal shift registers and
appears at DOUT 15.5 clock cycles later, clocked out
on the falling edge of CLK. When sending commands
to daisy-chained MAX6954s, all devices are accessed
at the same time. An access requires (16 x n) clock
cycles, where n is the number of MAX6954s connected

together. To update just one device in a daisy-chain,
the user can send the no-op command (0x00) to the
others. Figure 3 is the MAX6954 timing diagram.

The MAX6954 is written to using the following
sequence:

1) Take CLK low.

2) Take CS low. This enables the internal 16-bit shift

register.

3) Clock 16 bits of data into DIN, D15 first to D0 last,
observing the setup and hold times. Bit D15 is low,
indicating a write command.

4) Take CS high (while CLK is still high after clocking in
the last data bit).

5) Take CLK low.

Figure 4 shows a write operation when 16 bits are
transmitted.

If fewer or greater than 16 bits are clocked into the
MAX6954 between taking CS low and taking CS high
again, the MAX6954 stores the last 16 bits received,
including the previous transmission(s). The general
case is when n bits (where n > 16) are transmitted to
the MAX6954. The last bits are comprising bits {n-15} to
{n}, are retained, and are parallel loaded into the 16-bit
latch as bits D15 to D0, respectively (Figure 5).

DISPLAY TYPE

7 SEGMENT

(16-CHARACTER

HEXADECIMAL FONT)

14 SEGMENT/

16 SEGMENT

(104-CHARACTER ASCII FONT MAP)

DISCRETE LEDs

(DIRECT CONTROL)

Monocolor 16 8 128

Bicolor 8 4 64

Table 1. MAX6954 Drive Capability

1dp

2dp

fb

ec

d1

a1

i

l

g1 g2

hj

mk

a2

d2

dp dp

1a

1g

1f

1b

1e 1c

1d

2a

2g

2f 2b

2e 2c

2d

fb

ec

d

a

i

l

g1 g2

hj

mk

Figure 1. Segment Labeling for 7-Segment Display, 14-Segment Display, and 16-Segment Display

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

8 _______________________________________________________________________________________

Reading Device Registers

Any register data within the MAX6954 may be read by
sending a logic high to bit D15. The sequence is:

1) Take CLK low.

2) Take CS low. This enables the internal 16-bit shift

register.

3) Clock 16 bits of data into DIN, D15 first to D0 last.

D15 is high, indicating a read command and bits
D14 through D8 contain the address of the register

DIGIT

O18

0

f

ij

l

dp

1

f

ij

l

dp

2

f

ij

l

dp

3

f

ij

l

dp

4

f

ij

l

dp

5

f

ij

l

dp

6

f

ij

l

dp

7

f

ij

l

dp

Table 2. Connection Scheme for Eight 16-Segment Digits

Table 3. Connection Scheme for Eight 14-Segment Digits

D IG IT *

O0O1O2O3O4O5O6O7O8O9O10

O11

O12

O13

O14

O15

O16

O17

O18

0, 0a

2dp

1, 1a

2dp

2, 2a

2dp

3, 3a

2dp

4, 4a

2dp

5, 5a

2dp

6, 6a

2dp

7, 7a

2dp

Table 4. Connection Scheme for Sixteen 7-Segment Digits

D15

D14

D13

D12

D11

D10D9D8D7D6D5D4D3D2D1D0

R/W

ADDRESS

DATA

LSB

Table 5. Serial-Data Format (16 Bits)

*Each cathode driver output (CC0-CC7) connects to two digit common cathode pins.

O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17

CCO — a1 a2 b c d1 d2 e

— CC1 a1 a2 b c d1 d2 e

a1 a2 CC2 — b c d1 d2 e

a1 a2 — CC3 b c d1 d2 e

a1 a2 b c CC4 — d1 d2 e

a1 a2 b c — CC5 d1 d2 e

a1 a2 b c d1 d2 CC6 — e

a1 a2 b c d1 d2 — CC7 e

DIGIT O0 O1 O2 O3 O4 O5 O6 O7 O8 O9 O10 O11 O12 O13 O14 O15 O16 O17 O18

0 CCO — a — b c d — e f g1 g2 h i j k l m dp

1—CC1a—b c d—e fg1 g2 h i j k l m dp

2a—CC2 — b c d — e f g1 g2 h i j k l m dp

3a——CC3 b c d — e f g1 g2 h i j k l m dp

4a—bcCC4 — d — e f g1 g2 h i j k l m dp

5a—bc—CC5 d — e f g1 g2 h i j k l m dp

6a—bcd—CC6 — e f g1 g2 h i j k l m dp

7a—bcd——CC7 e f g1 g2 h i j k l m dp

g1 g2 h

g1 g2 h

g1 g2 h

g1 g2 h

g1 g2 h

g1 g2 h

g1 g2 h

g1 g2 h

k

k

k

k

k

k

k

k

m

m

m

m

m

m

m

m

C C 0— 1a — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

— CC1 1a — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

1a — CC2 — 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

1a — — CC3 1b 1c 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

1a — 1b 1c CC4 — 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

1a — 1b 1c — CC5 1d 1dp 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

1a — 1b 1c 1d 1dp CC6 — 1e 1f1g2a2b2c2d2e 2f2g

1a — 1b 1c 1d 1dp — CC7 1e 1f 1g 2a 2b 2c 2d 2e 2f 2g

MSB

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

_______________________________________________________________________________________ 9

to read. Bits D7 to D0 contain dummy data, which is
discarded.

4) Take CS high (while CLK is still high after clocking in

the last data bit), positions D7 through D0 in the shift
register are now loaded with the register data
addressed by bits D15 through D8.

5) Take CLK low.

6) Issue another read or write command (which can be
a no-op), and examine the bit stream at DOUT; the
second 8 bits are the contents of the register
addressed by bits D14 through D8 in step 3.

Digit Type Registers

The MAX6954 uses 32 digit registers to store the char­acters that the user wishes to display. These digit regis­ters are implemented with two planes, P0 and P1. Each
digit is represented by 2 bytes of memory, 1 byte in
plane P0 and the other in plane P1. The digit registers

are mapped so that a digit’s data can be updated in
plane P0, plane P1, or both planes at the same time
(Table 6).

If the blink function is disabled through the Blink Enable
Bit E (Table 19) in the configuration register, then the
digit register data in plane P0 is used to multiplex the
display. The digit register data in P1 is not used. If the
blink function is enabled, then the digit register data in
both plane P0 and plane P1 are alternately used to mul­tiplex the display. Blinking is achieved by multiplexing
the LED display using data plane P0 and plane P1 on
alternate phases of the blink clock (Table 20).

The data in the digit registers does not control the digit
segments directly for 14- and 16-segment displays.
Instead, the register data is used to address a charac­ter generator that stores the data for the 14- and 16­segment fonts (Tables 7 and 8). The lower 7 bits of the
digit data (D6 to D0) select the character from the font.

t

CSS

t

CL

t

CH

t

CP

t

CSH

t

CSW

t

DS

t

DH

D15

CLK

DIN

CS

D14 D1 D0

D15

t

DO

DOUT

Figure 3. Timing Diagram

MAX6954

DOUT

MICROCONTROLLER

CLK

DIN

MAX6954

MAX6954

CLK

DIN

CS

DOUT

CLK

DIN

CS

DOUT

CLK

DIN

CS

DOUT

CS

Figure 2. MAX6954 Daisy-Chain Connection

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

10 ______________________________________________________________________________________

The most significant bit of the register data (D7) con­trols the DP segment of the digits; it is set to 1 to light
DP, and to zero to leave DP unlit (Table 9).

For 7-segment displays, the digit plane data register
can be used to address a character generator, which
contains the data of a 16-character font containing the
hexadecimal font. The decode mode register can be
used to disable the character generator and allow the
segments to be controlled directly. Table 10 shows the
one-to-one pairing of each data bit to the appropriate
segment line in the digit plane data registers. The hexa­decimal font is decoded according to Table 11.

The digit-type register configures the display driver for
various combinations of 14-segment digits, 16-segment
digits, and/or pairs, or 7-segment digits. The function of
this register is to select the appropriate font for each
digit and route the output of the font to the appropriate
MAX6954 driver output pins. The MAX6954 has four
digit drive slots. A slot can be filled with various combi­nations of monocolor and bicolor 16-segment displays,
14-segment displays, or two 7-segment displays. Each
pair of bits in the register corresponds to one of the four

digit drive slots, as shown in Table 12. Each bit also cor­responds to one of the eight common-cathode digit
drive outputs, CC0 to CC7. When using bicolor digits,
the anode connections for the two digits within a slot are
always the same. This means that a slot correctly drives
two monocolor or one bicolor 14- or 16-segment digit.
The digit type register can be written, but cannot be
read. Examples of configuration settings required for
some display digit combinations are shown in Table 13.

7-Segment Decode-Mode Register

In 7-segment mode, the hexadecimal font can be dis­abled (Table 14). The decode-mode register selects
between hexadecimal code or direct control for each of
eight possible pairs of 7-segment digits. Each bit in the
register corresponds to one pair of digits. The digit
pairs are {digit 0, digit 0a} through {digit 7, digit 7a}.
Disabling decode mode allows direct control of the 16
LEDs of a dual 7-segment display. Direct control mode
can also be used to drive a matrix of 128 discrete
LEDs.

CS

CLK

DIN

D15 D14

D13

D12

D11 D10

D9

D8

D7

D6

D5

D4 D3 D2

D1

D0

DOUT

D15 = 0

Figure 4. Transmission of 16 Bits to the MAX6954

CS

CLK

DIN

BIT1BIT

2

N-9 N-8 N-7 N-6 N-5 N-4 N-3 N-2

DOUT

N-15

N-15 N-14 N-13 N-12 N-11 N-10 N-1

N-31 N-30 N-29 N-28 N-27 N-26 N-25 N-24

N-23

N-22 N-21 N-20 N-19

N-18

N-17 N-16

N

Figure 5. Transmission of More than 16 Bits to the MAX6954

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 11

A logic high selects hexadecimal decoding, while a
logic low bypasses the decoder. When direct control is
selected, the data bits D7 to D0 correspond to the seg­ment lines of the MAX6954. Write x0010000 to blank all
segments in hexadecimal decode mode.

Display Blink Mode

The display blinking facility, when enabled, makes the
driver flip automatically between displaying the digit
register data in planes P0 and P1. If the digit register
data for any digit is different in the two planes, then that
digit appears to flip between two characters. To make a
character appear to blink on or off, write the character
to one plane, and use the blank character (0x20) for the
other plane. Once blinking has been configured, it con­tinues automatically without further intervention.

Blink Speed

The blink speed is determined by the frequency of the
multiplex clock, OSC, and by the setting of the Blink
Rate Selection Bit B (Table 18) in the configuration reg­ister. The Blink Rate Selection Bit B sets either fast or
slow blink speed for the whole display.

Initial Power-Up

On initial power-up, all control registers are reset, the
display is blanked, intensities are set to minimum, and
shutdown is enabled (Table 15).

Configuration Register

The configuration register is used to enter and exit
shutdown, select the blink rate, globally enable and
disable the blink function, globally clear the digit data,
select between global or digit-by-digit control of intensi­ty, and reset the blink timing (Tables 16–19 and 21–24).

The configuration register contains 7 bits:

•S bit selects shutdown or normal operation
(read/write).

•B bit selects the blink rate (read/write).

•E bit globally enables or disables the blink function
(read/write).

•T bit resets the blink timing (data is not stored—tran­sient bit).

•R bit globally clears the digit data for both planes P0
and P1 for ALL digits (data is not stored—transient
bit).

•I bit selects between global or digit-by-digit control
of intensity (read/write).

•P bit returns the current phase of the blink timing
(read only—a write to this bit is ignored).

Character Generator Font Mapping

The font is composed of 104 characters in ROM. The
lower 7 bits of the 8-bit digit register represent the char­acter selection. The most significant bit, shown as x in
the ROM map of Tables 7 and 8, is 1 to light the DP
segment and zero to leave the DP segment unlit.

The character map follows the standard ASCII font for
96 characters in the x0101000 through x1111111
range. The first 16 characters of the 16-segment ROM
map cover 7-segment displays. These 16 characters
are numeric 0 to 9 and characters A to F (i.e., the hexa­decimal set).

Multiplex Clock and Blink Timing

The OSC pin can be fitted with capacitor C

SET

to GND
to use the internal RC multiplex oscillator, or driven by
an external clock to set the multiplex clock frequency
and blink rate. The multiplex clock frequency deter­mines the frequency that the complete display is updat­ed. With OSC at 4MHz, each display digit is enabled
for 200µs.

The internal RC oscillator uses an external resistor,
R

SET

, and an external capacitor, C

SET

, to set the oscil-

lator frequency. The suggested values of R

SET

(56kΩ)

and C

SET

(22pF) set the oscillator at 4MHz, which

makes the blink frequency 0.5Hz or 1Hz.

The external clock is not required to have a 50:50 duty
cycle, but the minimum time between transitions must
be 50ns or greater and the maximum time between
transitions must be 750ns.

The on-chip oscillator may be accurate enough for
applications using a single device. If an exact blink rate
is required, use an external clock ranging between
1MHz and 8MHz to drive OSC. The OSC inputs of multi­ple MAX6954s can be tied together to a common exter­nal clock to make the devices blink at the same rate.
The relative blink phasing of multiple MAX6954s can be
synchronized by setting the T bit in the control register
for all the devices in quick succession. If the serial inter­faces of multiple MAX6954s are daisy-chained by con­necting the DOUT of one device to the DIN of the next,
then synchronization is achieved automatically by
updating the configuration register for all devices simul­taneously. Figure 6 is the multiplex timing diagram.

OSC_OUT Output

The OSC_OUT output is a buffered copy of either the
internal oscillator clock or the clock driven into the OSC
pin if the external clock has been selected. The feature
is useful if the internal oscillator is used, and the user
wishes to synchronize other MAX6954s to the same
blink frequency. The oscillator is disabled while the
MAX6954 is in shutdown.

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

12 ______________________________________________________________________________________

Scan-Limit Register

The scan-limit register sets how many 14-segment dig­its or 16-segment digits or pairs of 7-segment digits are
displayed, from 1 to 8. A bicolor digit is connected as
two monocolor digits. The scan register also limits the
number of keys that can be scanned.

Since the number of scanned digits affects the display
brightness, the scan-limit register should not be used to
blank portions of the display (such as leading-zero sup­pression). Table 25 shows the scan-limit register format.

Intensity Registers

Digital control of display brightness is provided and
can be managed in one of two ways: globally or indi­vidually. Global control adjusts all digits together.
Individual control adjusts the digits separately.

The default method is global brightness control, which
is selected by clearing the global intensity bit (I data bit
D6) in the configuration register. This brightness setting
applies to all display digits. The pulse-width modulator
is then set by the lower nibble of the global intensity
register, address 0x02. The modulator scales the aver­age segment current in 16 steps from a maximum of
15/16 down to 1/16 of the peak current. The minimum
interdigit blanking time is set to 1/16 of a cycle. When
using bicolor digits, 256 color/brightness combinations
are available.

Individual brightness control is selected by setting the
global intensity bit (I data bit D6) in the configuration
register. The pulse-width modulator is now no longer
set by the lower nibble of the global intensity register,
address 0x02, and the data is ignored. Individual digi­tal control of display brightness is now provided by a
separate pulse-width modulator setting for each digit.
Each digit is controlled by a nibble of one of the four
intensity registers: intensity10, intensity32, intensity54,
and intensity76 for all display types, plus intensity10a,
intensity32a, intensity54a, and intensity76a for the extra
eight digits possible when 7-segment displays are
used. The data from the relevant register is used for
each digit as it is multiplexed. The modulator scales the
average segment current in 16 steps in exactly the
same way as global intensity adjustment.

Table 26 shows the global intensity register format,
Table 27 shows individual segment intensity registers,
Table 28 is the even individual segment intensity for­mat, and Table 29 is the odd individual segment inten­sity format.

GPIO and Key Scanning

The MAX6954 feature five general-purpose input/output
(GPIO) ports: P0 to P4. These ports can be individually
enabled as logic inputs or open-drain logic outputs.
The GPIO ports are not debounced when configured as
inputs. The ports can be read and the outputs set using
the 4-wire interface.

Some or all of the five ports can be configured to per­form key scanning of up to 32 keys. Ports P0 to P4 are
renamed Key_A, Key_B, Key_C, Key_D, and IRQ,
respectively, when used for key scanning. The full key­scanning configuration is shown in Figure 7. Table 30 is
the GPIO data register.

One diode is required per key switch. These diodes
can be common-anode dual diodes in SOT23 pack­ages, such as the BAW56. Sixteen diodes would be
required for the maximum 32-key configuration.

The MAX6954 can only scan the maximum 32 keys if
the scan-limit register is set to scan the maximum eight
digits. If the MAX6954 is driving fewer digits, then a
maximum of (4 x n) switches can be scanned, where n
is the number of digits set in the scan-limit register. For
example, if the MAX6954 is driving four 14-segment
digits cathode drivers O0 to O3 are used. Only 16 keys
can be scanned in this configuration; the switches
shown connected to O4 through O7 are not read.

If the user wishes to scan fewer than 32 keys, then
fewer scan lines can be configured for key scanning.
The unused Key_x ports are released back to their orig­inal GPIO functionality. If key scanning is enabled,
regardless of the number of keys being scanned, P4 is
always configured as IRQ (Table 31).

The key-scanning circuit utilizes the LEDs’ common­cathode driver outputs as the key-scan drivers. O0 to
07 go low for nominally 200µs (with OSC = 4MHz) in
turn as the displays are multiplexed. By varying the
oscillator frequency, the debounce time changes,
though key scanning still functions. Key_x inputs have
internal pullup resistors that allow the key condition to
be tested. The Key_x input is low during the appropri­ate digit multiplex period when the key is pressed. The
timing diagram of Figure 8 shows the normal situation
where all eight LED cathode drivers are used.

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 13

ADDRESS (COMMAND BYTE)

REGISTER

HEX CODE

No-Op

0000000 0x00

Decode Mode

0000001 0x01

Global Intensity

0000010 0x02

Scan Limit

0000011 0x03

Configuration

0000100 0x04

GPIO Data

0000101 0x05

Port Configuration

0000110 0x06

Display Test

0000111 0x07

Write KEY_A Mask
Read KEY_A Debounce

0001000 0x08

Write KEY_B Mask
Read KEY_B Debounce

0001001 0x09

Write KEY_C Mask
Read KEY_C Debounce

0001010 0x0A

Write KEY_D Mask
Read KEY_D Debounce

0001011 0x0B

Write Digit Type
Read KEY_A Pressed

0001100 0x0C

Read KEY_B Pressed* 1 0 0 0 1 1 0 1 0x0D
Read KEY_C Pressed* 1 0 0 0 1 1 1 0 0x0E
Read KEY_D Pressed* 1 0 0 0 1 1 1 1 0x0F
Intensity 10

0010000 0x10

Intensity 32

0010001 0x11

Intensity 54

0010010 0x12

Intensity 76

0010011 0x13

Intensity 10a (7 Segment Only)

0010100 0x14

Intensity 32a (7 Segment Only)

0010101 0x15

Intensity 54a (7 Segment Only)

0010110 0x16

Intensity 76a (7 Segment Only)

0010111 0x17

Digit 0 Plane P0

0100000 0x20

Digit 1 Plane P0

0100001 0x21

Digit 2 Plane P0

0100010 0x22

Digit 3 Plane P0

0100011 0x23

Digit 4 Plane P0

0100100 0x24

Digit 5 Plane P0

0100101 0x25

Digit 6 Plane P0

0100110 0x26

Digit 7 Plane P0

0100111 0x27

Digit 0a Plane P0 (7 Segment Only)

0101000 0x28

Digit 1a Plane P0 (7 Segment Only)

0101001 0x29

Digit 2a Plane P0 (7 Segment Only)

0101010 0x2A

Digit 3a Plane P0 (7 Segment Only)

0101011 0x2B

Table 6. Register Address Map

*Do NOT write to register.

D15 D14 D13 D12 D11 D10 D9 D8

R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W

R/W

R/W

R/W

R/W

R/W

R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

14 ______________________________________________________________________________________

ADDRESS (COMMAND BYTE)

REGISTER

HEX CODE

Digit 4a Plane P0 (7 Segment Only)

0101100 0x2C

Digit 5a Plane P0 (7 Segment Only)

0101101 0x2D

Digit 6a Plane P0 (7 Segment Only)

0101110 0x2E

Digit 7a Plane P0 (7 Segment Only)

0101111 0x2F

Digit 0 Plane P1

1000000 0x40

Digit 1 Plane P1

1000001 0x41

Digit 2 Plane P1

1000010 0x42

Digit 3 Plane P1

1000011 0x43

Digit 4 Plane P1

1000100 0x44

Digit 5 Plane P1

1000101 0x45

Digit 6 Plane P1

1000110 0x46

Digit 7 Plane P1

1000111 0x47

Digit 0a Plane P1 (7 Segment Only)

1001000 0x48

Digit 1a Plane P1 (7 Segment Only)

1001001 0x49

Digit 2a Plane P1 (7 Segment Only)

1001010 0x4A

Digit 3a Plane P1 (7 Segment Only)

1001011 0x4B

Digit 4a Plane P1 (7 Segment Only)

1001100 0x4C

Digit 5a Plane P1 (7 Segment Only)

1001101 0x4D

Digit 6a Plane P1 (7 Segment Only)

1001110 0x4E

Digit 7a Plane P1 (7 Segment Only)

1001111 0x4F

Write Digit 0 Planes P0 and P1 with Same
Data, Reads as 0x00

1100000 0x60

Write Digit 1 Planes P0 and P1 with Same
Data, Reads as 0x00

1100001 0x61

Write Digit 2 Planes P0 and P1 with Same
Data, Reads as 0x00

1100010 0x62

Write Digit 3 Planes P0 and P1 with Same
Data, Reads as 0x00

1100011 0x63

Write Digit 4 Planes P0 and P1 with Same
Data, Reads as 0x00

1100100 0x64

Write Digit 5 Planes P0 and P1 with Same
Data, Reads as 0x00

1100101 0x65

Write Digit 6 Planes P0 and P1 with Same
Data, Reads as 0x00

1100110 0x66

Write Digit 7 Planes P0 and P1 with Same
Data, Reads as 0x00

1100111 0x67

Write Digit 0a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101000 0x68

Write Digit 1a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101001 0x69

Table 6. Register Address Map (continued)

D15 D14 D13 D12 D11 D10 D9 D8

R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

R/W

The timing in Figure 8 loops over time, with 32 keys
experiencing a full key-scanning debounce over typi­cally 25.6ms. Four keys are sampled every 1.6ms, or
every multiplex cycle. If at least one key that was not
previously pressed is found to have been pressed dur­ing both sampling periods, then that key press is
debounced, and an interrupt is issued. The key-scan
circuit detects any combination of keys being pressed
during each debounce cycle (n-key rollover).

Port Configuration Register

The port configuration register selects how the five port
pins are used. The port configuration register format is
described in Table 32.

Key Mask Registers

The Key_A Mask, Key_B Mask, Key_C Mask, and
Key_D Mask write-only registers (Table 33) configure
the key-scanning circuit to cause an interrupt only when
selected (masked) keys have been debounced. Each
bit in the register corresponds to one key switch. The bit
is clear to disable interrupt for the switch, and set to
enable interrupt. Keys are always scanned (if enabled
through the port configuration register), regardless of
the setting of these interrupt bits, and the key status is
stored in the appropriate Key_x pressed register.

Key Debounced Registers

The Key_A debounced, Key_B debounced, Key_C
debounced, and Key_D debounced read-only registers
(Table 34) show which keys have been detected as
debounced by the key-scanning circuit.

Each bit in the register corresponds to one key switch.
The bit is set if the switch has been correctly
debounced since the register was read last. Reading a
debounced register clears that register (after the data
has been read) so that future keys pressed can be
identified. If the debounced registers are not read, the
key-scan data accumulates. However, as there is no
FIFO in the MAX6954, the user is not able to determine
key order, or whether a key has been pressed more
than once, unless the debounced key status registers
are read after each interrupt, and before the next key­scan cycle.

Reading any of the four debounced registers clears the
IRQ output. If a key is pressed and held down, the key
is reported as debounced (and IRQ issued) only once.
The key must be detected as released by the key-scan­ning circuit, before it debounces again. If the
debounced registers are being read in response to the
IRQ being asserted, then the user should generally read
all four registers to ensure that all the keys that were
detected by the key-scanning circuit are discovered.

Key Pressed Registers

The Key_A pressed, Key_B pressed, Key_C pressed,
and Key_D pressed read-only registers (Table 35)
show which keys have been detected as pressed by
the key-scanning circuit during the last test.

Each bit in the register corresponds to one key switch.
The bit is set if the switch has been detected as
pressed by the key-scanning circuit during the last test.

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 15

ADDRESS (COMMAND BYTE)

REGISTER

HEX CODE

Write Digit 2a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101010 0x6A

Write Digit 3a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101011 0x6B

Write Digit 4a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101100 0x6C

Write Digit 5a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101101 0x6D

Write Digit 6a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101110 0x6E

Write Digit 7a Planes P0 and P1 with Same
Data (7 Segment Only), Reads as 0x00

1101111 0x6F

Table 6. Register Address Map (continued)

Note: Unused register bits read as zero.

D15 D14 D13 D12 D11 D10 D9 D8

R/W

R/W

R/W

R/W

R/W

R/W

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

16 ______________________________________________________________________________________

DIGIT 1

ONE COMPLETE 1.6ms MULTIPLEX CYCLE AROUND 8 DIGITS

DIGIT 0's 200µs MULTIPLEX TIMESLOT

DIGIT 0

200µs

DIGIT 2 DIGIT 3 DIGIT 4 DIGIT 5 DIGIT 6 DIGIT 7

START OF
NEXT CYCLE

LOW

2/16TH

1/16TH

(MIN ON)

HIGH-Z

HIGH-Z

LOW

3/16TH

HIGH-Z

LOW

4/16TH

HIGH-Z

LOW

5/16TH

HIGH-Z

LOW

6/16TH

HIGH-Z

LOW

7/16TH

HIGH-Z

LOW

8/16TH

HIGH-Z

LOW

9/16TH

HIGH-Z

LOW

10/16TH

HIGH-Z

LOW

11/16TH

HIGH-Z

LOW

12/16TH

HIGH-Z

LOW

13/16TH

HIGH-Z

LOW

14/16TH

HIGH-Z

LOW

15/16TH

HIGH-Z

LOW

15/16TH

HIGH-Z

(MAX ON)

HIGH-Z

HIGH-Z

CURRENT SOURCE ENABLED

MINIMUM 12.5µs INTERDIGIT BLANKING INTERVAL

HIGH-Z

ANODE (LIT)

DIGIT 0 CATHODE
DRIVER INTENSITY
SETTINGS

ANODE (UNLIT)

Figure 6. Multiplex Timing Diagram (OSC = 4MHz)

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 17

LED OUTPUT O0

LED OUTPUT O1

LED OUTPUT O2

LED OUTPUT O3

LED OUTPUT O4

LED OUTPUT O5

LED OUTPUT O6

LED OUTPUT O7

12.5µs TO 187.5µs DIGIT PERIOD

1.6ms MULTIPLEX CYCLE 1 1.6ms MULTIPLEX CYCLE 2 1.6ms MULTIPLEX CYCLE 8

THE FIRST HALF OF A 25.6ms KEY-SCAN CYCLE

1.6ms MULTIPLEX CYCLE 8

THE SECOND HALF OF A 25.6ms KEY-SCAN CYCLE

1.6ms MULTIPLEX CYCLE 1

START OF NEXT KEY-SCAN CYCLE

FIRST TEST OF KEY SWITCHES SECOND TEST OF KEY SWITCHES

INTERRUPT ASSERTED IF REQUIRED
DEBOUNCE REGISTER UPDATED

C

A

A

B

DE

Figure 7. Key-Scanning Configuration

SW A0

SW A1

SW A2

SW A3

SW A4

SW A5

SW A6

SW A7

P0

V

CC

LED OUTPUT O0

LED OUTPUT O1

LED OUTPUT O2

LED OUTPUT O3

LED OUTPUT O4

LED OUTPUT O5

LED OUTPUT O6

LED OUTPUT O7

P1

P2

P3

P4

MICROCONTROLLER INTERRUPT

SW B0

SW B1

SW B2

SW B3

SW B4

SW B5

SW B6

SW B7

SW C0

SW C1

SW C2

SW C3

SW C4

SW C5

SW C6

SW C7

SW D0

SW D1

SW D2

SW D3

SW D4

SW D5

SW D6

SW D7

Figure 8. Key-Scan Timing Diagram

MAX6954

The bit is cleared if the switch has not been detected
as pressed by the key-scanning circuit during the last
test. Reading a pressed register does not clear that
register or clear the IRQ output.

Display Test Register

The display test register (Table 36) operates in two
modes: normal and display test. Display test mode
turns all LEDs on (including DPs) by overriding, but not
altering, all controls and digit registers (including the
shutdown register), except for the digit-type register
and the GPIO configuration register. The duty cycle,
while in display test mode, is 7/16 (see the Choosing
Supply Voltage to Minimize Power Dissipation section).

Selecting External Components R

SET

and

C

SET

to Set Oscillator Frequency and

Peak Segment Current

The RC oscillator uses an external resistor, R

SET

, and

an external capacitor, C

SET

, to set the frequency, f

OSC

.

The allowed range of f

OSC

is 1MHz to 8MHz. R

SET

also
sets the peak segment current. The recommended val­ues of R

SET

and C

SET

set the oscillator to 4MHz, which
makes the blink frequencies selectable between 0.5Hz
and 1Hz. The recommended value of R

SET

also sets
the peak current to 40mA, which makes the segment
current adjustable from 2.5mA to 37.5mA in 2.5mA
steps.

I

SEG

= KL/ R

SET

mA

f

OSC

= KF/ (R

SET

x C

SET

) MHz

where:

KL= 2240

KF= 5376

R

SET

= external resistor in kΩ

C

SET

= external capacitor in pF

C

STRAY

= stray capacitance from OSC pin to GND in

pF, typically 2pF

The recommended value of R

SET

is 56kΩ and the rec-

ommended value of C

SET

is 22pF.

The recommended value or R

SET

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

SET

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

The effective value of R

SET

includes not only the actual
external capacitor used, but also the stray capacitance
from OSC to GND. This capacitance is usually in the
1pF to 5pF range, depending on the layout used.

Applications Information

Driving Bicolor LEDs

Bicolor digits group a red and a green die together for
each display element, so that the element can be lit red
or green (or orange), depending on which die (or both)
is lit. The MAX6954 allows each segment’s current to
be set individually from the 1/16th (minimum current
and LED intensity) to 15/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 256
color/intensity combinations.

Choosing Supply Voltage to Minimize

Power Dissipation

The MAX6954 drives a peak current of 40mA into LEDs
with a 2.2V 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 -

2.2V) = 0.8V. If a higher supply voltage is used, the dri­ver absorbs a higher voltage, and the driver’s power
dissipation increases accordingly. However, if the LEDs
used have a higher forward voltage drop than 2.2V, the
supply voltage must be raised accordingly to ensure
that the driver always has at least 0.8V of headroom.

The voltage drop across the drivers with a nominal 5V
supply (5.0V - 2.2V) = 2.8V is nearly 3 times the drop
across the drivers with a nominal 3.3V supply (3.3V -

2.2V) = 1.1V. In most systems, consumption is an
important design criterion, and the MAX6954 should be
operated from the system’s 3.3V nominal supply. In
other designs, the lowest supply voltage may be 5V.
The issue now is to ensure the dissipation limit for the
MAX6954 is not exceeded. This can be achieved by
inserting a series resistor in the supply to the MAX6954,
ensuring that the supply decoupling capacitors are still
on the MAX6954 side of the resistor. For example, con­sider the requirement that the minimum supply voltage
to a MAX6954 must be 3.0V, and the input supply
range is 5V ±5%. Maximum supply current is 35mA +
(40mA x 17) = 715mA. Minimum input supply voltage is

4.75V. Maximum series resistor value is (4.75V -

3.0V)/0.715A = 2.44Ω. We choose 2.2Ω ±5%. Worst­case resistor dissipation is at maximum toleranced
resistance, i.e., (0.715A) 2 x (2.2Ω x 1.05) = 1.18W. The
maximum MAX6954 supply voltage is at maximum
input supply voltage and minimum toleranced resis­tance, i.e., 5.25V - (0.715A x 2.2Ω x 0.95) = 3.76V.

Low-Voltage Operation

The MAX6954 works over the 2.7V to 5.5V supply
range. The minimum useful supply voltage is deter­mined by the forward voltage drop of the LEDs at the

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

18 ______________________________________________________________________________________

peak current I

SEG

, plus the 0.8V headroom required by
the driver output stages. The MAX6954 correctly regu­lates I

SEG

with a supply voltage above this minimum
voltage. If the supply drops below this minimum volt­age, the driver output stages may brown out, and be
unable to regulate the current correctly. As the supply
voltage drops further, the LED segment drive current
becomes effectively limited by the output driver's on­resistance, and the LED drive current drops. The char­acteristics of each individual LED in a display digit are
well matched, so the result is that the display intensity
dims uniformly as supply voltage drops out of regula­tion and beyond.

Computing Power Dissipation

The upper limit for power dissipation (PD) for the
MAX6954 is determined from the following equation:

PD= (V+ x 35mA) + (V+ - V

LED

) (DUTY x I

SEG

x N)

where:

V+ = supply voltage

DUTY = duty cycle set by intensity register

N = number of segments driven (worst case is 17)

V

LED

= LED forward voltage at I

SEG

I

SEG

= segment current set by R

SET

PD= Power dissipation, in mW if currents are in mA

Dissipation example:

I

SEG

= 30mA, N = 17, DUTY = 15/16,

V

LED

= 2.4V at 30mA, V+ = 3.6V

P

D

= 3.6V (35mA) + (3.6V - 2.4V)(15/16 x

30mA x 17) = 0.700W

Thus, for a 36-pin SSOP package (T

JA

= 1 / 0.0118 =
+85°C/W from Operating Ratings), the maximum
allowed ambient temperature TAis given by:

T

J(MAX)

= TA+ (PDx TJA) = +150°C
= TA+ (0.700 x +85°C/W)

So TA= +90.5°C. Thus, the part can be operated safely
at a maximum package temperature of +85°C.

Power Supplies

The MAX6954 operates from a single 2.7V to 5.5V
power supply. Bypass the power supply to GND with a

0.1µF capacitor as close to the device as possible. Add
a 47µF capacitor if the MAX6954 is not close to the
board's input bulk decoupling capacitor.

Terminating the Serial Interface

The MAX6954 uses fixed voltage thresholds of 0.6V
and 1.8V for the 4-wire interface inputs. These fixed
thresholds allow the MAX6954 to be controlled by a
host operating from a lower supply voltage than the
MAX6954; for example, 2.5V. The fixed thresholds also
reduce the logic input noise margin when operating the
MAX6954 from a higher supply voltage, such as 5V. At
higher supply voltages, it may be necessary to fit termi­nation components to the CLK, DIN, and CS inputs to
avoid signal reflections that the MAX6954 could
respond to as multiple transitions. Suitable termination
components can be either a 33pF capacitor or 4.7kΩ
resistor fitted from each of the CLK, DIN, and CS inputs
to GND.

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 19

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

20 ______________________________________________________________________________________

x000 x010 x011 x100 x101 x110 x111x001

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

MSB

LSB

Table 7. 16-Segment Display Font Map

x000 x010 x011 x100 x101 x110 x111x001

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

.

MSB

LSB

Table 8. 14-Segment Display Font Map

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 21

REGISTER DATA

MODE

ADDRESS

CODE

(HEX)

D0

14-segment or 16-segment mode, writing digit data
to use font map data with decimal place unlit

0 Bits D6 to D0 select font characters 0 to 127

14-segment or 16-segment mode, writing digit data
to use font map data with decimal place lit

1 Bits D6 to D0 select font characters 0 to 127

7-segment decode mode, DP unlit

0000 D3 to D0

7-segment decode mode, DP lit

1000 D3 to D0

7-segment no-decode mode

Direct control of 8 segments

Table 9. Digit Plane Data Register Format

REGISTER DATA

MODE

ADDRESS CODE

(HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Segment Line

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

dp a b c d e f g

Table 10. Segment Decoding for 7-Segment Displays

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

0x20 to 0x2F
0x40 to 0x4F
0x60 to 0x6F

D7 D6 D5 D4 D3 D2 D1

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

22 ______________________________________________________________________________________

REGISTER

DATA

ON SEGMENTS = 1

7-SEGMENT

CHARACTER

D7*

D6, D5,

D4

DP*

G

0—X0000—

0

1—X0001—

0

2—X0010—

1

3—X0011—

1

4—X0100—

1

5—X0101—

1

6—X0110—

1

7—X0111—

0

8—X1000—

1

9—X1001—

1

A—X1010—

1

B—X1011—

1

C—X1100—

0

D—X1101—

1

E—X1110—

1

F—X1111—

10001

1

1

Table 11. 7-Segment Segment Mapping Decoder for Hexadecimal Font

REGISTER DATA

DIGIT-TYPE

REGISTER

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Output Drive Line

CC0

Slot Identification

0x0C

Slot 4 Slot 3 Slot 2 Slot 1

Table 12. Digit-Type Register

*The decimal point is set by bit D7 = 1.

D3 D2 D1 D0

CC7 CC6 CC5 CC4 CC3 CC2 CC1

ABC DE F

111 111
011 000
110 110
111 100
011 001
101 101
101 111
111 000
111 111
111 101
111 011
001 111
100 111
011 110
100 111

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 23

REGISTER DATA

DECODE

MODE

ADDRESS

CODE

(HEX)

HEX

CODE

No decode for digit pairs 7 to 0. 0x01 00000000 0x00
Hexadecimal decode for digit pair 0,
no decode for digit pairs 7 to 1.

0x01 00000001 0x01

Hexadecimal decode for digit pairs 2 to 0,
no decode for digit pairs 7 to 3.

0x01 00000111 0x07

Hexadecimal decode for digit pairs 7 to 0.

0x01 11111111 0xFF

Table 14. Decode-Mode Register Examples

REGISTER DATA

DIGIT-TYPE

REGISTER SETTING

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Digits 7 to 0 are 16-segment or 7­segment digits.

0x0C 00000000

Digit 0 is a 14-segment digit,
digits 7 to 1 are 16-segment or 7­segment digits.

0x0C 00000001

Digits 2 to 0 are 14-segment
digits, digits 7 to 3 are 16­segment or 7-segment digits.

0x0C 00000111

Digits 7 to 0 are 14-segment
digits.

0x0C 11111111

Table 13. Example Configurations for Display Digit Combinations

D7 D6 D5 D4 D3 D2 D1 D0

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

24 ______________________________________________________________________________________

REGISTER DATA

REGISTER

POWER-UP
CONDITION

CODE

(HEX)

D0

Decode Mode Decode mode enabled 0x01

1

Global Intensity 1/16 (min on) 0x02

0

Scan Limit Display 8 digits: 0, 1, 2, 3, 4, 5, 6, 7 0x03

1

Control Register

Shutdown enabled, blink speed is
slow, blink disabled

0x04

0

GPIO Data Outputs are low 0x05

0

Port Configuration

No key scanning, P0 to P4 are all
inputs

0x06

1

Display Test Normal operation 0x07

0

Key_A Mask None of the keys cause interrupt 0x08

0

Key_B Mask None of the keys cause interrupt 0x09

0

Key_C Mask None of the keys cause interrupt 0x0A

0

Key_D Mask None of the keys cause interrupt 0x0B

0

Digit Type All are 16 segment or 7 segment 0x0C

0

Intensity10 1/16 (min on) 0x10

0

Intensity32 1/16 (min on) 0x11

0

Intensity54 1/16 (min on) 0x12

0

Intensity76 1/16 (min on) 0x13

0

Intensity10a 1/16 (min on) 0x14

0

Intensity32a 1/16 (min on) 0x15

0

Intensity54a 1/16 (min on) 0x16

0

Intensity76a 1/16 (min on) 0x17

0

Digit 0 Blank digit, both planes 0x60

0

Digit 1 Blank digit, both planes 0x61

0

Digit 2 Blank digit, both planes 0x62

0

Digit 3 Blank digit, both planes 0x63

0

Digit 4 Blank digit, both planes 0x64

0

Digit 5 Blank digit, both planes 0x65

0

Digit 6 Blank digit, both planes 0x66

0

Digit 7 Blank digit, both planes 0x67

0

Digit 0a Blank digit, both planes 0x68

0

Digit 1a Blank digit, both planes 0x69

0

Digit 2a Blank digit, both planes 0x6A

0

Digit 3a Blank digit, both planes 0x6B

0

Digit 4a Blank digit, both planes 0x6C

0

Digit 5a Blank digit, both planes 0x6D

0

Digit 6a Blank digit, both planes 0x6E

0

Digit 7a Blank digit, both planes 0x6F

0

Key_A Debounced No key presses have been detected 0x88

0

Key_B Debounced No key presses have been detected 0x89

0

Key_C Debounced

No key presses have been detected 0x8A

0

Key_D Debounced

No key presses have been detected 0x8B

0

Key_A Pressed Keys are not pressed 0x8C

0

Key_B Pressed Keys are not pressed 0x8D

0

Key_C Pressed Keys are not pressed 0x8E

0

Key_D Pressed Keys are not pressed 0x8F

0

Table 15. Initial Power-Up Register Status

ADDRESS

D7 D6 D5 D4 D3 D2 D1

1 111111
X XXX000
X XXXX11

00XX000

XXX0000

0 001111

X XXXXXX
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 010000
0 010000
0 010000
0 010000
0 010000
0 010000
0 010000
0 010000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000
0 000000

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 25

REGISTER DATA

MODE

D0

Configuration
Register

S

Table 16. Configuration Register Format

REGISTER DATA

MODE

D0

Shutdown

0

Normal
Operation

1

Table 17. Shutdown Control (S Data Bit DO)
Format

REGISTER DATA

MODE

D0

Slow blinking. Segments blink on for 1s, off for 1s with f

OSC

= 4MHz.

I

S

Fast blinking. Segments blink on for 0.5s, off for 0.5s with f

OSC

= 4MHz.

I

S

Table 18. Blink Rate Selection (B Data Bit D2) Format

REGISTER DATA

MODE

D7 D6 D5 D4 D3 D2 D1 D0

Blink function is disabled. P I R T 0 B X S
Blink function is enabled. P I R T 1 B X S

Table 19. Global Blink Enable/Disable (E Data Bit D3) Format

SEGMENT’S BIT SETTING

IN PLANE P1

SEGMENT’S BIT SETTING

IN PLANE P0

SEGMENT

BEHAVIOR

00Segment off.

01

Segment on only during the 1st half of each
blink period.

10

Segment on only during the 2nd half of each
blink period.

11Segment on.

Table 20. Digit Register Mapping with Blink Globally Enabled

REGISTER DATA

MODE

D0

Blink timing counters are unaffected. P I R 0 E B X S
Blink timing counters are reset on the rising edge of CS.PIR1EBXS

Table 21. Global Blink Timing Synchronization (T Data Bit D4) Format

REGISTER DATA

MODE

Digit data for both planes P0 and P1 are unaffected.

I

Digit data for both planes P0 and P1 are cleared on the rising edge of CS.

I

Table 22. Global Clear Digit Data (R Data Bit D5) Format

D7 D6 D5 D4 D3 D2 D1

PIRTEBX

D7 D6 D5 D4 D3 D2 D1

P

P

D7 D6 D5 D4 D3 D2 D1

PIRTEBX

PIRTEBX

RTE0X

RTE1X

D7 D6 D5 D4 D3 D2 D1

D7 D6 D5 D4 D3 D2 D1 D0

P

P

0TEBXS

1TEBXS

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

26 ______________________________________________________________________________________

REGISTER DATA

MODE

D0

Intensity for all digits is controlled by one setting in the global intensity register.

S

Intensity for digits is controlled by the individual settings in the intensity10 and
intensity76 registers.

S

Table 23. Global Intensity (I Data Bit D6) Format

REGISTER DATA

MODE

D7 D6 D5 D4 D3 D2 D1 D0

P1 Blink Phase 0 I R T E B X S
P0 Blink Phase 1 I R T E B X S

Table 24. Blink Phase Readback (P Data Bit D7) Format

REGISTER DATA

SCAN

LIMIT

ADDRESS CODE

(HEX)

HEX

CODE

Display Digit 0 only 0x03 X X X X X 0 0 0 0x00

Display Digits 0 and 1 0x03 X X X X X 0 0 1 0x01

Display Digits 0 1 2 0x03 X X X X X 0 1 0 0x02

Display Digits 0 1 2 3 0x03 X X X X X 0 1 1 0x03

Display Digits 0 1 2 3 4 0x03 X X X X X 1 0 0 0x04

Display Digits 0 1 2 3 4 5 0x03 X X X X X 1 0 1 0x05

Display Digits 0 1 2 3 4 5 6 0x03 X X X X X 1 1 0 0x06

Display Digits 0 1 2 3 4 5 6 7 0x03 X X X X X 1 1 1 0x07

Table 25. Scan-Limit Register Format

REGISTER DATA

DUTY

CYCLE

TYPICAL

SEGMENT

ADDRESS

D7

HEX

CODE

1/16 (min on) 2.5 0x02 X X X X 0 0 0 0 0xX0

2/16 5 0x02 X X X X 0 0 0 1 0xX1

3/16 7.5 0x02 X X X X 0 0 1 0 0xX2

4/16 10 0x02 X X X X 0 0 1 1 0xX3

5/16 12.5 0x02 X X X X 0 1 0 0 0xX4

6/16 15 0x02 X X X X 0 1 0 1 0xX5

7/16 17.5 0x02 X X X X 0 1 1 0 0xX6

8/16 20 0x02 X X X X 0 1 1 1 0xX7

9/16 22.5 0x02 X X X X 1 0 0 0 0xX8

10/16 25 0x02 X X X X 1 0 0 1 0xX9

11/16 27.5 0x02 X X X X 1 0 1 0 0xXA

12/16 30 0x02 X X X X 1 0 1 1 0xXB

13/16 32.5 0x02 X X X X 1 1 0 0 0xXC

14/16 35 0x02 X X X X 1 1 0 1 0xXD

15/16 37.5 0x02 X X X X 1 1 1 0 0xXE

15/16 (max on)

37.5 0x02 X X X X 1 1 1 1 0xXF

Table 26. Global Intensity Register Format

D7 D6 D5 D4 D3 D2 D1

P0RTEBX

P1RTEBX

D7 D6 D5 D4 D3 D2 D1 D0

CURRENT (mA)

CODE (HEX)

D6 D5 D4 D3 D2 D1 D0

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 27

REGISTER DATA

REGISTER

FUNCTION

ADDRESS

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Intensity10 Register 0x10 Digit 1 Digit 0

Intensity32 Register 0x11 Digit 3 Digit 2

Intensity54 Register 0x12 Digit 5 Digit 4

Intensity76 Register 0x13 Digit 7 Digit 6

Intensity10a Register 0x14 Digit 1a (7 segment only) Digit 0a (7 segment only)

Intensity32a Register 0x15 Digit 3a (7 segment only) Digit 2a (7 segment only)

Intensity54a Register 0x16 Digit 5a (7 segment only) Digit 4a (7 segment only)

Intensity76a Register 0x17 Digit 7a (7 segment only) Digit 6a (7 segment only)

Table 27. Individual Segment Intensity Registers

REGISTER DATA

DUTY

CYCLE

TYPICAL

SEGMENT

ADDRESS

CODE
(HEX)

HEX

CODE

1/16 (min on) 2.5 0x10 to 0x17 0000

0xX0

2/16 5 0x10 to 0x17 0001

0xX1

3/16 7.5 0x10 to 0x17 0010

0xX2

4/16 10 0x10 to 0x17 0011

0xX3

5/16 12.5 0x10 to 0x17 0100

0xX4

6/16 15 0x10 to 0x17 0101

0xX5

7/16 17.5 0x10 to 0x17 0110

0xX6

8/16 20 0x10 to 0x17 0111

0xX7

9/16 22.5 0x10 to 0x17 1000

0xX8

10/16 25 0x10 to 0x17 1001

0xX9

11/16 27.5 0x10 to 0x17 1010

0xXA

12/16 30 0x10 to 0x17 1011

0xXB

13/16 32.5 0x10 to 0x17 1100

0xXC

14/16 35 0x10 to 0x17 1101

0xXD

15/16 37.5 0x10 to 0x17 1110

0xXE

15/16 (max on) 37.5 0x10 to 0x17

See Table 29.

1111

0xXF

Table 28. Even Individual Segment Intensity Format

CURRENT (mA)

D7 D6 D5 D4 D3 D2 D1 D0

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

28 ______________________________________________________________________________________

REGISTER DATA

DUTY

CYCLE

TYPICAL

SEGMENT

ADDRESS

CODE

(HEX)

HEX

CODE

1/16 (min on) 2.5 0x10 to 0x17 0 0 0 0

0x0X

2/16 5 0x10 to 0x17 0 0 0 1

0x1X

3/16 7.5 0x10 to 0x17 0 0 1 0

0x2X

4/16 10 0x10 to 0x17 0 0 1 1

0x3X

5/16 12.5 0x10 to 0x17 0 1 0 0

0x4X

6/16 15 0x10 to 0x17 0 1 0 1

0x5X

7/16 17.5 0x10 to 0x17 0 1 1 0

0x6X

8/16 20 0x10 to 0x17 0 1 1 1

0x7X

9/16 22.5 0x10 to 0x17 1 0 0 0

0x8X

10/16 25 0x10 to 0x17 1 0 0 1

0x9X

11/16 27.5 0x10 to 0x17 1 0 1 0

0xAX

12/16 30 0x10 to 0x17 1 0 1 1

0xBX

13/16 32.5 0x10 to 0x17 1 1 0 0

0xCX

14/16 35 0x10 to 0x17 1 1 0 1

0xDX

15/16 37.5 0x10 to 0x17 1 1 1 0

0xEX

15/16 (max on) 37.5 0x10 to 0x17 1 1 1 1

See Table 28.

0xFX

Table 29. Odd Individual Segment Intensity Format

REGISTER DATA

MODE

ADDRESS

D7 D6 D5 D4 D3 D2 D1 D0

Write GPIO Data 0x05 X X X P4 P3 P2 P1 P0

Read GPIO Data

0x85 0 0 0

P3 P2 P1 P0

Table 30. GPIO Data Register

KEYS

SCANNED

PORTS

AVAILABLE

P0 P1 P2 P3 P4

None 5 pins GPIO GPIO GPIO GPIO GPIO

1 to 8 3 pins Key_A GPIO GPIO GPIO IRQ

9 to 16 2 pins Key_A Key_B GPIO GPIO IRQ

17 to 24 1 pin Key_A Key_B Key_C GPIO IRQ

25 to 36 None Key_A Key_B Key_C Key_D IRQ

Table 31. Port Scanning Function Allocation

CURRENT (mA)

CODE (HEX)

D7 D6 D5 D4 D3 D2 D1 D0

P4 or IRQ status

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 29

REGISTER DATA

MODE

ADDRESS

D7 D6 D5 D4 D3 D2 D1 D0

GPIO
Configuration
Register

0x06 Set number of keys scanned

Set port direction for ports P0 to P4:
0 = output, 1 = input

PORT ALLOCATION OPTIONS

0 Keys Scanned 0x06 0 0 0 P4 P3 P2 P1 P0
8 Keys Scanned 0x06 0 0 1 IRQ P3 P2 P1

Key_A

16 Keys Scanned

0x06 0 1 0 IRQ P3 P2

Key_A

24 Keys Scanned

0x06 0 1 1 IRQ P3

Key_A

32 Keys Scanned

0x06 1 X X IRQ

Key_A

EXAMPLE PORT CONFIGURATION SETTINGS

No Keys
Scanned, P4 and
P2 Are Outputs,

Others Are Inputs

0x06 00001011

8 Keys Scanned,
P3 and P1 Are
Outputs, P2 Is an
Input

0x06 0 0 1 X 0 1 0 X

32 Keys
Scanned, No
GPIO Ports

0x06 1 XXXXXXX

Table 32. Port Configuration Register Format

REGISTER DATA

WITH APPROPRIATE SWITCH NAMED BELOW

KEY

MASK

REGISTER

ADDRESS

CODE

(HEX

D7 D6 D5 D4 D3 D2 D1 D0

Key_A Mask

Register

0x08

SW_A0

Key_B Mask

Register

0x09

SW_B0

Key_C Mask

Register

0x0A

SW_C0

Key_D Mask

Register

0x0B

SW_D0

Table 33. Key Mask Register Format

CODE (HEX)

Key_B

Key_C Key_B

Key_D Key_C Key_B

SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1

SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1

SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1

SW_ D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

30 ______________________________________________________________________________________

REGISTER DATA

KEY

DEBOUNCED

REGISTER

ADDRESS

CODE

(HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Key_A

Debounced

Register

0x88

SW_A0

Key_B

Debounced

Register

0x89

SW_B0

Key_C

Debounced

Register

0x8A

SW_C0

Key_D

Debounced

Register

0x8B

SW_D0

Table 34. Key Debounced Register Format

REGISTER DATA

KEY

PRESSED

REGISTER

ADDRESS

CODE

(HEX

D7 D6 D5 D4 D3 D2 D1 D0

Key_A

Pressed

Register

0x8C

SW_A0

Key_B

Pressed

Register

0x8D

SW_B0

Key_C

Pressed

Register

0x8E

SW_C0

Key_D

Pressed

Register

0x8F

SW_D0

Table 35. Key Pressed Register Format

REGISTER DATA

MODE

ADDRESS

CODE

(HEX)

D7 D6 D5 D4 D3 D2 D1 D0

Normal Operation 0x07 X XXXXXX0

Display Test 0x07 X XXXXXX 1

Table 36. Display Test Register

SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1

SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1

SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1

SW_D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1

SW_A7 SW_A6 SW_A5 SW_A4 SW_A3 SW_A2 SW_A1

SW_B7 SW_B6 SW_B5 SW_B4 SW_B3 SW_B2 SW_B1

SW_C7 SW_C6 SW_C5 SW_C4 SW_C3 SW_C2 SW_C1

SW_D7 SW_D6 SW_D5 SW_D4 SW_D3 SW_D2 SW_D1

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 31

C O N F I G U R A T IO N

C H O IC E

CC0: 16-seg monocolor

CC1: 16-seg monocolor

CC0 and CC1:

(2) 7-seg bicolor

or (4) 7-seg monocolor

or (1) 7-seg bicolor

and (2) 7-seg monocolor*

CC0 and CC1:

(1)16-seg bicolor

CC0: 16-seg monocolor

CC0: (2) 7-seg monocolor*

or 7-seg bicolor

CC1: 14-seg monocolor

CC0: 14-seg monocolor

CC1: 16-seg monocolor

CC1: (2) 7-seg monocolor*

or 7-seg bicolor

CC0 and CC1: (2) 14-seg

monocolor or 14-seg

bicolor

00

— CC0

—

—— CC0

01

CC1

——

—

CC1

02

1a a1 a1 1a a a a1 1a a

03

— a2 a2 — — — a2 — —

04 bb 1b bb1bbbb1b b

05 cc 1c cc1cccc1c c

06

1d d1 d1 1d d d d1 1d d

07

1dp d2 d2 1dp — — d2

—

08 ee 1e ee1eeee1e e

09 ff 1f ff1ffff1f f

010

1g g1 g1 1g g1 g1 g1 1g g1

011

2a g2 g2 2a g2 g2 g2 2a g2

012 hh 2b hh2bhhh2b h

013 ii 2c ii2ciii2c i

014 jj 2d jj2djjj2d k

015 kk 2e kk2ekkk2e l

016 ll 2f ll2flll2f l

017 mm 2g mm2gmmm2g m

018

2dp dp dp 2dp dp dp dp

dp

ADDRESS

CODE (HEX)

0x0C

D7

D6

See Table 40.

D5

D4

See Table 39.

D3

D2

See Table 38.

D1

0101

REGISTER DATA

D0 0 0 1 1

Table 37. Slot 1 Configuration

*7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).

**The highlighted row is used in Typical Operating Circuit 1 for display digits 0 and 1.

C o m m o n - C a t h o d e

D r i v e : D ig it Ty p e

CC0

— CC1

a1 a1

a2 a2

d1 d1

d2 d2

g1 g1

g2 g2

dp dp

CC0 CC0 CC0

CC1

CC0

CC1

CC1 CC1

1dp

2dp

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

32 ______________________________________________________________________________________

*7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).

**The highlighted row is used in Typical Operating Circuit 1 for display digits 2 and 3.

C O N F I G U R A T IO N

C H O IC E

C o m m o n - C a t h o d e

D r i v e : D ig it Ty p e

CC2: 16-seg monocolor

CC3: 16-seg monocolor

CC2 and CC3:

(2) 7-seg bicolor

or (4) 7-seg monocolor

or (1) 7-seg bicolor

and (2) 7-seg monocolor*

CC2 and CC3:

(1)16-seg bicolor

CC2: 16-seg monocolor

CC2: (2) 7-seg monocolor*

or 7-seg bicolor

CC3: 14-seg monocolor

CC2: 14-seg monocolor

CC3: 16-seg monocolor

CC3: (2) 7-seg monocolor*

or 7-seg bicolor

CC2 and CC3: (2) 14-seg

monocolor or 14-seg

bicolor

00

1a a1 a1 1a a a a1 1a a

01

—a2a2———a2— —

02

— CC2

—

—— CC2

03

CC3

——

—

CC3

04 bb 1b b b 1b b b b 1b b

05 cc 1c c c 1c c c c 1c c

06

1d d1 d1 1d d d d1 1d d

07

1dp d2 d2 1dp — — d2

—

08 ee 1e e e 1e e e e 1e e

09 ff 1f f f 1f f f f 1f f

010

1g g1 g1 1g g1 g1 g1 1g g1

011

2a g2 g2 2a g2 g2 g2 2a g2

012 hh 2b h h 2b h h h 2b h

013 ii 2c i i 2c i i i 2c i

014 jj 2d j j 2d j j j 2d k

015 kk 2e k k 2e k k k 2e l

016 ll 2f l l 2f l l l 2f l

017 mm 2g m m 2g m m m 2g m

018

2dp dp dp 2dp dp dp dp

dp

ADDRESS

CODE (HEX)

0x0C

D7

D6

See Table 40.

D5

D4

See Table 39.

D3

0101

D2 0 0 1 1

D1

REGISTER DATA

D0

See Table 37.

Table 38. Slot 2 Configuration

a1 a1

a2 a2

CC2

— CC3

CC2 CC2 CC2

CC3

CC3

CC2

CC3 CC3

d1 d1

d2 d2

g1 g1

g2 g2

dp dp

1dp

2dp

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 33

C O N F I G U R A T IO N

C H O IC E

C o m m o n - C a t h o d e

D r i v e : D ig it Ty p e

CC4: 16-seg monocolor

CC5: 16-seg monocolor

CC4 and CC5:

(2) 7-seg bicolor

or (4) 7-seg monocolor

or (1) 7-seg bicolor

and (2) 7-seg monocolor*

CC4 and CC5:

(1)16-seg bicolor

CC4: 16-seg monocolor

CC4: (2) 7-seg monocolor*

or 7-seg bicolor

CC5: 14-seg monocolor

CC4: 14-seg monocolor

CC5: 16-seg monocolor

CC5: (2) 7-seg monocolor*

or 7-seg bicolor

CC4 and CC5: (2) 14-seg

monocolor or 14-seg

bicolor

00

1a a1 a1 1a a a a1 1a a

01

—a2a2———a2——

02 b b 1b b b 1b b b b 1b b

03 c c 1c c c 1c c c c 1c c

04

— CC4

—

—— CC4

05

CC5

——

—

CC5

06

1d d1 d1 1d d d d1 1d d

07

1dp d2 d2 1dp — — d2

—

08 e e 1e e e 1e e e e 1e e

09 f f 1f f f 1f f f f 1f f

010

1g g1 g1 1g g1 g1 g1 1g g1

011

2a g2 g2 2a g2 g2 g2 2a g2

012 h h 2b h h 2b h h h 2b h

013 i i 2c i i 2c i i i 2c i

014 j j 2d j j 2d j j j 2d k

015 k k 2e k k 2e k k k 2e l

016 l l 2f l l 2f l l l 2f l

017 m m 2g m m 2g m m m 2g m

018

2dp dp dp 2dp dp dp dp

dp

ADDRESS

CODE (HEX)

0x0C

D7

D6

See Table 40.

D5

0101

D4 0 0 1 1

D3

D2

See Table 38.

D1

REGISTER DATA

D0

See Table 37.

Table 39. Slot 3 Configuration

*7-segment digits can be replaced by directly controlled discrete LEDs according to settings in decode mode register (Table 11).

**The highlighted row is used in Typical Operating Circuit 1 for display digits 4 and 5.

a1 a1

a2 a2

CC4

— CC5

d1 d1

d2 d2

g1 g1

g2 g2

dp dp

CC4 CC4 CC4

CC5

CC4

CC5

CC5 CC5

1dp

2dp

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

34 ______________________________________________________________________________________

*7-segment digits can be replaced by directly controlled discrete LEDs according to settings in the decode mode register (Table 11).

**The highlighted row is used in Typical Operating Circuit 1 for display digits 6 and 7.

C O N F I G U R A T IO N

C H O IC E

C o m m o n - C a t h o d e

D r i v e : D ig it Ty p e

CC6: 16-seg monocolor

CC7: 16-seg monocolor

CC6 and CC7:

(2) 7-seg bicolor

or (4) 7-seg monocolor

or (1) 7-seg bicolor

and (2) 7-seg monocolor*

CC6 and CC7:

(1)16-seg bicolor

CC6: 16-seg monocolor

CC6: (2) 7-seg monocolor*

or 7-seg bicolor

CC7: 14-seg monocolor

CC6: 14-seg monocolor

CC7: 16-seg monocolor

CC7: (2) 7-seg monocolor*

or 7-seg bicolor

CC6 and CC7: (2) 14-seg

monocolor or 14-seg

bicolor

00

1a a1 a1 1a a a a1 1a a

01

— a2 a2 — — — a2 — —

02 bb 1b bb1bbbb1b b

03 cc 1c cc1cccc1c c

04

1d d1 d1 1d d d d1 1d d

05

1dp d2 d2 1dp — — d2

—

06

— CC6

—

—— CC6

07

CC7

——

—

CC7

08 ee 1e ee1eeee1e e

09 ff 1f ff1ffff1f f

010

1g g1 g1 1g g1 g1 g1 1g g1

011

2a g2 g2 2a g2 g2 g2 2a g2

012 hh 2b hh2bhhh2b h

013 ii 2c ii2ciii2c i

014 jj 2d jj2djjj2d k

015 kk 2e kk2ekkk2e l

016 ll 2f ll2flll2f l

017 mm 2g mm2gmmm2g m

018

2dp dp dp 2dp dp dp dp

dp

ADDRESS

CODE (HEX)

0x0C

D7

0101

D6 0 0 1 1

D5

D4

See Table 39.

D3

D2

See Table 38.

D1

REGISTER DATA

D0

See Table 37.

Table 40. Slot 4 Configuration

a1 a1

a2 a2

d1 d1

d2 d2

CC6

— CC7

CC6 CC6 CC6

CC7

CC7

1dp

CC6

CC7 CC7

g1 g1

g2 g2

dp dp

2dp

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 35

f

a

Rcc

dp

g

Gcc

b
c

e

d

DIGIT 0b (RED), DIGIT 1b (GREEN)

7-SEGMENT BICOLOR LED

O16
O17
O18
O0
O1

O11
O12
O13
O14

O0
O2
O3
O4

O15

f

a

h

g2

g1

i

b
c

e

d

DIGITS 2 AND 3

14-SEGMENT BICOLOR

DIGIT 6

4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs

O8
O9
O10
O11
O12

O0
O4
O5
O6

m

Rcc

dp

Ccc

j

l

k
O16
O17
O18
O2
O3

O13
O14
O15

f

a

CC1

dp

g

CC0

b
c

e

d

DIGITS 0a AND 1a

7-SEGMENT MONOCOLOR

O9
O10
O7

O1
O0

O2
O4
O5
O6
O8

d2

a1

g1

f

e

g2

a2
b

d1

c

DIGIT 5

16-SEGMENT MONOCOLOR

O6
O7
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O5

O11
O12
O13

d2

a1

g1

f

e

g2

a2

b

d1

c

DIGIT 4

16-SEGMENT MONOCOLOR

O6
O7
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O4

O11
O12
O13

3.3V

100nF

47µF

O0

O1

O2

O3

O4

O5

O6

O7

O8

O9

O10

O11

O12

O13

O14

O15

O16

O17

O18

P0

P1

P2

P3

P4

ISET

56kΩ

OSC_OUT

OSC

V+
V+

GND

GND

DOUT

V+

GND

DIN

CLK

CS

BLINK

O5
O8
O9
O10

O11
O12
O13
O14

O15
O16
O17
O18

O6

22pF

O0
O2
O3
O4

DIGIT 7

4 x 4 MATRIX OF DISCRETE MONOCOLOR LEDs

O5
O8
O9
O10

O11
O12
O13
O14

O15
O16
O17
O18

O7

MAX6954

Typical Operating Circuits

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

36 ______________________________________________________________________________________

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 0

O6
O7
O8
O9
O10

O2
O3
O4
O5

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O0

O11
O12
O13

d2

a

g1

f

e

g2

a2

b

d1

c

DIGIT 2

O6
O7
O8
O9
O10

O0
O1
O4
O5

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O2

O11
O12
O13

3.3V

100nF

47µF

O0

O1

O2

O3

O4

O5

O6

O7

O8

O9

O10

O11

O12

O13

O14

O15

O16

O17

O18

P0

P1

P2

P3

P4

ISET

OSC_OUT

OSC

V+
V+

GND

GND

DOUT

V+

GND

DIN

CLK

CS

BLINK

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 1

O6
O7
O8
O9
O10

O2
O3
O4
O5

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O1

O11
O12
O13

d2

a

g1

f

e

g2

a2

b

d1

c

DIGIT 3

O6
O7
O8
O9
O10

O0
O1
O4
O5

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O3

O11
O12
O13

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 6

O4
O5
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O6

O11
O12
O13

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 7

O4
O5
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O7

O11
O12
O13

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 4

O6
O6
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O4

O11
O12
O13

d2

a

g1

f

e

g2

a2
b

d1

c

DIGIT 5

O6
O7
O8
O9
O10

O0
O1
O2
O3

k

m

l

dp

h

j

i
O14
O15
O16
O17
O18

cc

O5

O11
O12
O13

MAX6954

56kΩ

22pF

Typical Operating Circuits (continued)

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display

Driver with I/O Expander and Key Scan

______________________________________________________________________________________ 37

40

N.C.

V+

OSC

V+

39

38

37

36

35

34

33

32

31

1

2

3

4

5

6

7

8

9

10

N.C.

GND

GND

ISET

GND

TOP VIEW

MAX6954APL

30

29

28

27

26

25

24

23

22

21

11

12

13

14

15

16

17

18

19

PDIP

20

SSOP

MAX6954AAX

1

2

3

4

5

6

7

8

9

10

11

12

13

14

O7

O6

O5

O4

O3

O2

O1

O0

DIN

CLK

DOUT

CS

P1

P0

15

16

17

18GND

ISET

GND

O8

36

35

34

33

32

31

30

29

28

27

26

25

24

23

P4

P3

P2

OSC_OUT

BLINK

O18

O10

O17

O16

O15

O14

O13

O12

O11

22

21

20

19 V+

O9

P4

P3

P2

OSC_OUT

BLINK

O18

O10

O17

O16

O15

O14

O13

O12

O11

O9

OSC

V+

O7

O6

O5

O4

O3

O2

O1

O0

DIN

CLK

DOUT

CS

P1

P0

O8

V+

Pin Configurations

Chip Information

TRANSISTOR COUNT: 57,480

PROCESS: CMOS

MAX6954

4-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan

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.

38 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.

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.)

SSOP.EPS

PACKAGE OUTLINE, 36L SSOP, 0.80 MM PITCH

1

1

21-0040 E

REV.DOCUMENT CONTROL NO.APPROVAL

PROPRIETARY INFORMATION

TITLE:

FRONT VIEW

MAX

0.011

0.104

0.017

0.299

0.013

INCHES

0.291

0.009

E

C

DIM

0.012

0.004

B

A1

MIN

0.096A

0.23

7.40 7.60

0.32

MILLIMETERS

0.10

0.30

2.44

MIN

0.44

0.29

MAX

2.65

0.040

0.020L

0.51 1.02

H0.4140.398 10.11 10.51

e 0.0315 BSC 0.80 BSC

D0.6120.598

15.20 15.55

HE

A1

A

D

e

B

0∞-8∞

L

C

TOP VIEW

SIDE VIEW

1

36