MAX6957ATL+ ,4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O ExpanderFeatures®The MAX6957 compact, serial-interfaced LED display ● High-Speed 26MHz SPI-/QSPI™-/MICROWI ..
MAX6957ATL+ ,4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O ExpanderElectrical Characteristics(Typical Operating Circuit, V+ = 2.5V to 5.5V, T = T to T , unless otherw ..
MAX6957ATL+T ,4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O ExpanderMAX6957 4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O Expander
MAX6958AAEE ,2-Wire Interfaced, 3V to 5.5V, 4-Digit, 9-Segment LED Display Drivers with KeyscanApplicationsSCL 5VSCLIRQ IRQ/SEG9 V+Set-Top BoxesAudio/Video EquipmentMAX6959Panel Meters INPUT1Ven ..
MAX6958AAEE+ ,2-Wire Interfaced, 3V to 5.5V, 4-Digit, 9-Segment LED Display Drivers with KeyscanApplicationsSEG0–SEG8SCL 5VSCLSet-Top Boxes IRQ V+Audio/Video Equipment IRQ/SEG9Panel Meters MAX695 ..
MAX6958AAEE+T ,2-Wire Interfaced, 3V to 5.5V, 4-Digit, 9-Segment LED Display Drivers with KeyscanELECTRICAL CHARACTERISTICS(V+ = 3V to 5.5V, T = T to T , unless otherwise noted. Typical values are ..
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB401 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts
MB40166 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MB40176 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MB40176 ,AD/DA CONVERTERFUJITSU SEMICONDUCTORDS04-28500-5EDATA SHEETASSPAD/DA CONVERTERMB40166/MB401761-CHANNEL 6-BIT AD/DA ..
MAX6957AAI+-MAX6957AAX+-MAX6957ANI+-MAX6957ATL-MAX6957ATL+-MAX6957ATL+T
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and 28-Port LED Display Driver and I/O Expander
Typical operating Circuit appears at end of data sheet.QSPI is a trademark of Motorola, Inc.
MICROWIRE is a registered trademark of National
Semiconductor Corp.
General DescriptionThe MAX6957 compact, serial-interfaced LED display
driver general-purpose I/O (GPIO) peripheral provides
microprocessors with up to 28 ports. Each port is indi-
vidually user configurable to either a logic input, logic
output, or common-anode (CA) LED constant-current
segment driver. Each port configured as an LED seg-
ment 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 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 MAX6957 is controlled
through an SPI-compatible 4-wire serial interface.
The MAX6957AAX and MAX6957ATL have 28 ports and
are available in 36-pin SSOP and 40-pin TQFN (6mm x
6mm) packages, respectively. The MAX6957AAI and
MAX6957ANI have 20 ports and are available in 28-pin
SSOP and 28-pin DIP packages, respectively.
For a 2-wire interfaced version, refer to the MAX6956
data sheet.
For a lower cost pin-compatible port expander without
the constant-current LED drive capability, refer to the
MAX7301 data sheet.
Applications●Set-Top Boxes●Panel Meters●White Goods●Bar Graph Displays●Industrial Controllers●System Monitoring
Features● High-Speed 26MHz SPI-/QSPI™-/MICROWIRE®-
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
Pin Configurations continued at end of data sheet.
*Exposed pad.
PARTTEMP RANGEPIN-
PACKAGEMAX6957ANI-40°C to +125°C28 DIP
MAX6957AAI-40°C to +125°C28 SSOP
MAX6957AAX-40°C to +125°C36 SSOP
MAX6957ATL-40°C to +125°C40 TQFN-EP*
SCLK
DIN
P31
P30
P22
P29
P28
P27
P26
P25
P24
P23
P21
P20
P19
P18
P17
P16
P15
P14
P13
P12
DOUT
GND
GND
ISET
SSOP/DIPTOP VIEW
MAX6957
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Conigurations
Ordering Information
Voltage (with Respect to GND)
V+ ............................................................................-0.3V to +6V
All Other pins ...............................................-0.3V to (V+ + 0.3V)
P4–P31 Current ...............................................................±30mA
GND Current ....................................................................800mA
Continuous Power Dissipation (TA = +70°C)28-Pin PDIP (derate 14.3mW/°C above +70°C) .......1143mW28-Pin SSOP (derate 9.1mW/°C above +70°C) ..........727mW36-Pin SSOP (derate 11.8mW/°C above +70°C) ........941mW40-Pin TQFN (derate 37.0mW/°C above +70°C) ......2963mW
Operating Temperature Range (TMIN, TMAX) ....-40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Supply VoltageV+2.55.5V
Shutdown Supply CurrentISHDNAll digital inputs at
V+ or GND
TA = +25°C5.58TA = -40°C to +85°C10
TA = TMIN to TMAX11
Operating Supply CurrentIGPOH
All ports programmed
As outputs high, no load,
All other inputs at V+ or
GND
TA = +25°C180230TA = -40°C to +85°C250
TA = TMIN to TMAX270
Operating Supply CurrentIGPOL
All ports programmed
As outputs low, no load,
All other inputs at V+ or
GND
TA = +25°C170210TA = -40°C to +85°C230
TA = TMIN to TMAX240
Operating Supply CurrentILED
All ports programmed
as LED outputs, all LEDs
off, no load, all other
inputs at V+ or GND
TA = +25°C110135TA = -40°C to +85°C140
TA = TMIN to TMAX145
INPUTS AND OUTPUTSLogic-High Input Voltage
Port InputsVIH0.7 ×V
Logic-Low Input Voltage
Port InputsVIL0.3 ×V
Input Leakage CurrentIIH, IILGPIO inputs without pullup,
VPORT = V+ to GND-100±1+100nA
GPIO Input Internal Pullup to V+IPU
V+ = 2.5V121930V+ = 5.5V80120180
Hysteresis Voltage GPIO InputsDVI0.3V
Output High VoltageVOH
GPIO outputs, ISOURCE = 2mA, TA = -40°C to
+85°C
V+ -
0.7V
GPIO outputs, ISOURCE = 1mA,
V+ -
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Electrical CharacteristicsStresses 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.
Absolute Maximum Ratings
Note 1: All parameters tested at TA = +25°C. Specifications over temperature are guaranteed by design.
Note 2: Guaranteed by design.
3(V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
(Typical Operating Circuit, V+ = 2.5V to 5.5V, TA = TMIN to TMAX, unless otherwise noted.) (Note 1)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSCLK Clock PeriodtCP38.4ns
CLK Pulse Width HightCH19ns
CLK Pulse Width LowtCL19ns
CS Fall to SCLK Rise Setup TimetCSS9.5ns
CLK Rise to CS Rise Hold TimetCSH0ns
DIN Setup TimetDS9.5ns
DIN Hold TimetDH0ns
Output Data Propagation DelaytDOCLOAD = 25pF21ns
Minimum CS Pulse HightCSW19ns
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSPort Sink CurrentIOLVPORT = 0.6V21018mA
Output Short-Circuit CurrentIOLSCPort conigured output low, shorted to V+2.751120mA
Port Drive LED Sink Current,Port Conigured as LED DriverIPORT
V+ = 2.5V, VLED = 2.3V at maximum LED
current9.513.518V+ = 3.3V, VLED = 2.4V at maximum LED
current (Note 2)18.52427.5
V+ = 5.5V, VLED = 2.4V at maximum LED
current192530
Port Drive Logic Sink Current,Port Conigured as LED DriverIPORT_SC
V+ = 2.5V, VOUT = 0.6V at maximum LED
current18.52328.0
V+ = 5.5V, VOUT = 0.6V at maximum LED
current192428
Port LED Sink Current Matching∆IPORT6%
Input High-Voltage SCLK, DIN,VIHV+ ≤ 3.3V1.6VV+ > 3.3V2
Input Low-Voltage SCLK, DIN, CSVIL0.6V
Input Leakage Current SCLK,
DIN, CSIIH, IIL-50+50nA
Output High-Voltage DOUTVOHISOURCE = 1.6mAV+ -
0.5V
Output Low-Voltage DOUTVOLISINK = 1.6mA0.4V
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Timing Characteristics (Figure 3)
Electrical Characteristics (continued)
(RISET = 39kΩ, TA = +25°C, unless otherwise noted.)
GPO SHORT-CIRCUIT CURRENT
vs. TEMPERATUREMAX6957 toc09
PORT CURRENT (mA)
GPO = 0, PORT
SHORTED TO V+
GPO = 1, PORT
SHORTED TO GND
GPI PULLUP CURRENT
vs. TEMPERATUREMAX6957 toc08
PULLUP CURRENT (A)
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
GPO SOURCE CURRENT vs. TEMPERATURE
(OUTPUT = 1)MAX6957 toc07
PORT SOURCE CURRENT (mA)
VPORT = 1.4V
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
GPO SINK CURRENT vs. TEMPERATURE
(OUTPUT = 0)MAX6957 toc06
TEMPERATURE (°C)
PORT SINK CURRENT (mA)
V+ = 2.5V TO 5.5V, VPORT = 0.6V
LED DRIVER SINK CURRENT
vs. TEMPERATUREMAX6957 toc05
TEMPERATURE (°C)
PORT SINK CURRENT (mA)
VLED = 2.4V
V+ = 5.5V
V+ = 3.3V
LED DRIVER SINK CURRENT vs. V+MAX6957 toc04
V+ (V)
PORT SINK CURRENT (mA)
LED DROP = 2.4V
LED DROP = 1.8V
OPERATING SUPPLY CURRENT vs. V+
(NO LOADS)MAX6957 toc03
V+ (V)
SUPPLY CURRENT (mA)
ALL PORTS LED (ON)
ALL PORTS LED (OFF)
ALL PORTS OUTPUT (1)
ALL PORTS OUTPUT (0)
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATUREMAX6957 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (A)
V+ = 5.5V
V+ = 3.3V
V+ = 2.5V
OPERATING SUPPLY CURRENT
vs. TEMPERATUREMAX6957 toc01
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
V+ = 2.5V TO 5.5V
NO LOAD
ALL PORTS
OUTPUT (1)
ALL PORTS
OUTPUT (0)
ALL PORTS LED (OFF)
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Typical Operating Characteristics
Detailed DescriptionThe MAX6957 LED driver/GPIO peripheral provides up
to 28 I/O ports, P4 to P31, controlled through an SPI-
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
MAX6957 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 seg-
ment current for all segments, with a maximum of 24mA
per segment. The MAX6957 drives any combination of
discrete LEDs and CA digits, including seven-segment
and starburst alphanumeric types.
Figure 1 is the MAX6957 functional diagram. Any I/O
port can be configured as a push-pull output (sink-
ing 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
A detected transition is flagged through an interrupt pin
(port P31).
The Typical Operating Circuit shows two MAX6957s
working together controlling three monocolor 16-seg-
ment-plus-DP displays, with five ports left available for
GPIO (P27–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 MAX6957AAX has 28 ports, P4 to P31. The
28-pin MAX6957ANI and MAX6957AAI make only 20
ports available. The eight unused ports should be con-
figured as outputs on power-up by writing 0x55 to reg-
isters 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.
PIN
NAMEFUNCTION28 SSOP
28 PDIP36 SSOP40 TQFN136ISETSegment Current Setting. Connect ISET to GND through a resistor (RISET) to set
the maximum segment current.
2, 32, 337, 38,GNDGround440DOUT4-Wire Serial Data Output Port
5–24——P12–P31LED Segment Drivers and GPIO. P12 to P31 can be conigured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.5–32
1–10,
12–19,
P4–P31LED Segment Drivers and GPIO. P4 to P31 can be conigured as CA LED drivers,
GPIO outputs, CMOS logic inputs, or CMOS logic inputs with weak pullup resistor.3332SCLK4-Wire Serial Clock Input Port3433DIN4-Wire Serial Data Input Port3534CS4-Wire Chip-Select Input, Active-Low3635V+Positive Supply Voltage. Bypass V+ to GND with a minimum 0.047µF capacitor.—11, 20,N.C.No Connection. Not internally connected.—EPEPExposed Pad. Internally connected to GND. Connect to large ground plane for
maximum thermal dissipation. Do not use as sole ground connection.
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Pin Description
Register Control of I/O Ports and LEDs
Across Multiple DriversThe MAX6957 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 exam-
ple: seven, 7-segment digits (Figure 2). This example
requires two MAX6957s, with one digit being driven by
both devices, half by one MAX6957, half by the other
(digit 4 in this example). The two drivers are static,
and therefore do not need to be synchronized. The
MAX6957 sees CA digits as multiple discrete LEDs. To
simplify access to displays that overlap two MAX6957s,
the MAX6957 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 sec-
ond 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 nonexis-
tent, 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 byte-writes, 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
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.
Table 2. Port Configuration Matrix
Table 1. Port Configuration Map
MODEFUNCTION
PORT
REGISTER
(0x20–0x5F)
(0xA0–0xDF)
PIN BEHAVIORADDRESS
CODE (HEX)
PORT
CONFIGURATION
BIT PAIR
UPPERLOWEROutputLED Segment Driver
Register bit = 0High impedance
0x09 to 0x0F00Register bit = 1
Open-drain current sink, with sink
current (up to 24mA) determined
by the appropriate current register
OutputGPIO OutputRegister bit = 0Active-low logic output0x09 to 0x0F01Active-high logic output
InputGPIO Input
Without PullupRegister bit =
input logic level
Schmitt logic input0x09 to 0x0F10
InputGPIO Input with PullupSchmitt logic input with pullup0x09 to 0x0F11
REGISTERADDRESS CODE (HEX)
REGISTER DATAD6D5D4D3D2D1D0Port Configuration for P7, P6, P5, P40x09P7P6P5P4
Port Configuration for P11, P10, P9, P80x0AP11P10P9P8
Port Configuration for P15, P14, P13, P120x0BP15P14P13P12
Port Configuration for P19, P18, P17, P160x0CP19P18P17P16
Port Configuration for P23, P22, P21, P200x0DP23P22P21P20
Port Configuration for P27, P26, P25, P240x0EP27P26P25P24
Port Configuration for P31, P30, P29, P280x0FP31P30P29P28
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
ShutdownWhen the MAX6957 is in shutdown mode, all ports are
forced to inputs, 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 MAX6957 is taken out of shutdown. The display driv-
er 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 6). Shutdown mode is temporarily overridden by
the display test function.
Serial InterfaceThe MAX6957 communicates through an SPI-compati-
ble 4-wire serial interface. The interface has three
inputs, Clock (SCLK), 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
SCLK. DOUT provides a copy of the bit that was input
15.5 clocks earlier, or upon a query it outputs internal
register data, and is stable on the rising edge of SCLK.
Note that the SPI protocol expects DOUT to be high impedance when the MAX6957 is not being accessed; DOUT on the MAX6957 is never high imped-
ance. Go to www.maximintegrated.com/an1879 for ways to convert DOUT to tri-state, if required.SCLK and DIN may be used to transmit data to other
peripherals, so the MAX6957 ignores all activity on
SCLK and DIN except between the fall and subsequent
rise of CS.
Figure 1. MAX6957 Functional DiagramD1D2D3D4D5D6D7D8D9D10D11D12D13D14D15D1D2D3D4D5D6D7D8D9D10D11D12D13D14D15
R/WDATA
TEST REGISTER
INTENSITY REGISTERS
PORT REGISTERS
LED DRIVERS AND GPIO
INTENSITY
CONFIGURATION
TEST
P4 TO P31
LED DRIVERS
OR GPIO
SEGMENT OR
GPIO DATAR/W
CONFIGURATION
REGISTERSPORT CHANGE
DETECTOR
MASK REGISTER
COMMAND
REGISTER DECODE8
DATA BYTECOMMAND BYTE
DIN
SCLK
DOUT
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Figure 3. 4-Wire Interface Timing
Figure 2. Two MAX6957s Controlling Seven 7-Segment Displays
tCSHtCL
tCSStCHtCSH
SCLK
DIN
DOUT
tDS
tDH
tDVtDOP1P2P3P4P5P6P7P8P9P10P11P12P13P14P15P16P17P18P19P20P21P22P23P24P25P26P27P28P29P30P31P1P2P3P4P5P6P7P8P9P10P11P12P13P14P15P16P17P18P19P20P21P22P23P24P25P26P27P28P29P30P31
7-SEGMENT DIGIT 1
VIRTUAL SEGMENTS
VIRTUAL SEGMENTS
7-SEGMENT DIGIT 57-SEGMENT DIGIT 67-SEGMENT DIGIT 7
7-SEGMENT DIGIT 27-SEGMENT DIGIT 37-SEGMENT DIGIT 4V+
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Control and Operation Using the 4-Wire InterfaceControlling the MAX6957 requires sending a 16-bit word.
The first byte, D15 through D8, is the command address
(Table 3), and the second byte, D7 through D0, is the data
byte (Table 4).
Connecting Multiple MAX6957s
to the 4-Wire BusMultiple MAX6957s may be daisy-chained by connect-
ing the DOUT of one device to the DIN of the next, and
driving SCLK and CS lines in parallel (Figure 4). 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 SCLK. When sending commands to
multiple MAX6957s, all devices are accessed at the same
time. An access requires (16 × n) clock cycles, where n is
the number of MAX6957s connected together. To update
just one device in a daisy-chain, the user can send the
No-Op command (0x00) to the others.
Writing Device Registers The MAX6957 contains a 16-bit shift register into which
DIN data are clocked on the rising edge of SCLK, when
CS is low. When CS is high, transitions on SCLK have no
effect. When CS goes high, the 16 bits in the Shift register
are parallel loaded into a 16-bit latch. The 16 bits in the
latch are then decoded and executed.
The MAX6957 is written to using the following sequence:
1) Take SCLK low.
2) Take CS low. This enables the internal 16-bit shift
register.
3) Clock 16 bits of data into DIN—D15 first, D0 last—
observing the setup and hold times (bit D15 is low,
indicating a write command).
4) Take CS high (either while SCLK is still high after
clocking in the last data bit, or after taking SCLK low).
5) Take SCLK low (if not already low).
Figure 5 shows a write operation when 16 bits are
transmitted.
Figure 5. 16-Bit Write Transmission to the MAX6957
Figure 4. Daisy-Chain Arrangement for Controlling Multiple MAX6957s
D15
= 0D14D13D12D11D10D9D8D7D6D5D4D3D2D1D0
D15 = 0
SCLK
DIN
DOUT
MICROCONTROLLERSERIAL DATA OUTPUT
SERIAL CLOCK OUTPUT
SERIAL DATA INPUT
DIN
SCLK
DOUTDIN
SCLK
DOUTDIN
SCLK
DOUT
SERIAL CS OUTPUTMAX6957MAX6957MAX6957
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
It is acceptable to clock more than 16 bits into the
MAX6957 between taking CS low and taking CS high
again. In this case, only the last 16 bits clocked into the
MAX6957 are retained.
Reading Device RegistersAny register data within the MAX6957 may be read by
sending a logic high to bit D15. The sequence is:
1) Take SCLK low.
2) Take CS low (this enables the internal 16-bit shift reg-
ister).
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 containing the address of the register to
be read. Bits D7–D0 contain dummy data, which is
discarded.
4) Take CS high (either while SCLK is still high after
clocking in the last data bit, or after taking SCLK low),
positions D7 through D0 in the Shift register are now
loaded with the register data addressed by bits D1
through D8.
5) Take SCLK low (if not already 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 D1 through D8 in step 3.
Initial Power-UpOn initial power-up, all control registers are reset, cur-
rent registers are set to minimum value, and the
MAX6957 enters shutdown mode (Table 4).
LED Current ControlLED 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 one register, 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 (Table7). The global current register (0x02) data are
then ignored, and segment currents are set using register
addresses 0x12 through 0x1F (Tables 10, 11, and 12).
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 6). A detected
active-high interrupt output (INT). Note that the MAX6957
does not identify which specific port(s) caused the inter-
rupt, but provides an alert that one or more port levels
have changed.
The mask register contains 7 mask bits that select which
of the seven ports P24–P30 are to be monitored (Table
13). 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 regard-
less 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.
Port P31 must be configured as an output in order to work
as the interrupt output INT when transition detection is
used. Port P31 is set as output by writing bit D7 = 0 and
bit D6 = 1 to the port configuration register (Table 1).
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 8). Whenever the config-
uration register is written with the M bit set, the MAX6957
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 snap-
shot 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 with the M
bit clear, or a transition is detected. The INT output port
P31 goes low, if it was not already low.
Once transition detection is enabled, the MAX6957 con-
tinuously 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), INT output port P31 is latched high. The INT
output is 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 13).
Transition detection is a one-shot event. When INT has
been cleared after responding to a transition event, tran-
sition 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.
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 3. Register Address Map
REGISTERCOMMAND ADDRESSHEX
CODED15D14D13D12D11D10D9D8No-OpR/W 00000000x00
Global Current R/W00000100x02
Configuration R/W00001000x04
Transition Detect MaskR/W00001100x06
Display TestR/W00001110x07
Port Configuration P7, P6, P5, P4R/W00010010x09
Port Configuration P11, P10, P9, P8R/W00010100x0A
Port Configuration P15, P14, P13, P12R/W00010110x0B
Port Configuration P19, P18, P17, P16R/W00011000x0C
Port Configuration P23, P22, P21, P20R/W00011010x0D
Port Configuration P27, P26, P25, P24R/W00011100x0E
Port Configuration P31, P30, P29, P28R/W00011110x0F
Current054R/W00100100x12
Current076R/W00100110x13
Current098R/W00101000x14
Current0BAR/W00101010x15
Current0DCR/W00101100x16
Current0FER/W00101110x17
Current110R/W00110000x18
Current132R/W00110010x19
Current154R/W00110100x1A
Current176R/W00110110x1B
Current198R/W00111000x1C
Current1BAR/W00111010x1D
Current1DCR/W00111100x1E
Current1FER/W00111110x1F
Port 0 only (virtual port, no action)R/W01000000x20
Port 1 only (virtual port, no action)R/W01000010x21
Port 2 only (virtual port, no action)R/W01000100x22
Port 3 only (virtual port, no action)R/W01000110x23
Port 4 only (data bit D0. D7–D1 read as 0)R/W01001000x24
Port 5 only (data bit D0. D7–D1 read as 0)R/W01001010x25
Port 6 only (data bit D0. D7–D1 read as 0)R/W01001100x26
Port 7 only (data bit D0. D7–D1 read as 0)R/W01001110x27
Port 8 only (data bit D0. D7–D1 read as 0)R/W01010000x28
Port 9 only (data bit D0. D7–D1 read as 0)R/W01010010x29
Port 10 only (data bit D0. D7–D1 read as 0)R/W01010100x2A
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 3. Register Address Map (continued)
REGISTER COMMAND ADDRESSHEX
CODED15D14D13D12D11D10D9D8Port 11 only (data bit D0. D7–D1 read as 0)R/W01010110x2B
Port 12 only (data bit D0. D7–D1 read as 0)R/W01011000x2C
Port 13 only (data bit D0. D7–D1 read as 0)R/W01011010x2D
Port 14 only (data bit D0. D7–D1 read as 0)R/W01011100x2E
Port 15 only (data bit D0. D7–D1 read as 0)R/W01011110x2F
Port 16 only (data bit D0. D7–D1 read as 0)R/W01100000x30
Port 17 only (data bit D0. D7–D1 read as 0)R/W01100010x31
Port 18 only (data bit D0. D7–D1 read as 0)R/W01100100x32
Port 19 only (data bit D0. D7–D1 read as 0)R/W01100110x33
Port 20 only (data bit D0. D7–D1 read as 0)R/W01101000x34
Port 21 only (data bit D0. D7–D1 read as 0)R/W01101010x35
Port 22 only (data bit D0. D7–D1 read as 0)R/W01101100x36
Port 23 only (data bit D0. D7–D1 read as 0)R/W01101110x37
Port 24 only (data bit D0. D7–D1 read as 0)R/W01110000x38
Port 25 only (data bit D0. D7–D1 read as 0)R/W01110010x39
Port 26 only (data bit D0. D7–D1 read as 0)R/W01110100x3A
Port 27 only (data bit D0. D7–D1 read as 0)R/W01110110x3B
Port 28 only (data bit D0. D7–D1 read as 0)R/W01111000x3C
Port 29 only (data bit D0. D7–D1 read as 0)R/W01111010x3D
Port 30 only (data bit D0. D7–D1 read as 0)R/W01111100x3E
Port 31 only (data bit D0. D7–D1 read as 0)R/W01111110x3F
4 ports 4–7 (data bits D0–D3. D4–D7 read as 0))R/W10000000x40
5 ports 4–8 (data bits D0–D4. D5–D7 read as 0)R/W10000010x41
6 ports 4–9 (data bits D0–D5. D6–D7 read as 0)R/W10000100x42
7 ports 4–10 (data bits D0–D6. D7 reads as 0)R/W10000110x43
8 ports 4–11 (data bits D0–D7)R/W10001000x44
8 ports 5–12 (data bits D0–D7)R/W10001010x45
8 ports 6–13 (data bits D0–D7)R/W10001100x46
8 ports 7–14 (data bits D0–D7)R/W10001110x47
8 ports 8–15 (data bits D0–D7)R/W10010000x48
8 ports 9–16 (data bits D0–D7)R/W10010010x49
8 ports 10–17 (data bits D0–D7)RW10010100x4A
8 ports 11–18 (data bits D0–D7)R/W10010110x4B
8 ports 12–19 (data bits D0–D7)R/W10011000x4C
8 ports 13–20 (data bits D0–D7)R/W10011010x4D
8 ports 14–21 (data bits D0–D7)R/W10011100x4E
8 ports 15–22 (data bits D0–D7)R/W10011110x4F
MAX69574-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
