The MAX6326/MAX6327/MAX6328/MAX6346/MAX6347/MAX6348 microprocessor (µP) supervisory circuits monitor the power supplies in µP and digital systems. These devices provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 2.5V, 3V, 3.3V, and 5V powered circuits.These circuits perform a single function: they assert a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 100ms after VCC has risen above the reset threshold. The only difference between the devices is their output. The MAX6326/MAX6346 (push-pull) and MAX6328/MAX6348 (open-drain) have an active-low reset output. The MAX6327/MAX6347 have an active-high push-pull reset output. All of these parts are guaranteed to be in the correct state for VCC down to 1V. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds are factory-trimmable between 2.2V and 4.63V, in approximately 100mV increments. Twenty-one standard versions are available. Contact the factory for availability of nonstandard versions.Ultra-low supply currents (1µA max for the MAX6326/MAX6327/MAX6328) make these parts ideal for use in portable equipment. All six devices are available in space-saving SOT23 and SC70 packages.ApplicationsComputers: Desktop, Workstation, ServerControllersCritical µP and µC Power MonitoringIntelligent InstrumentsPortable Battery-Powered Equipment

The MAX6326/MAX6327/MAX6328/MAX6346/MAX6347/MAX6348 microprocessor (µP) supervisory circuits monitor the power supplies in µP and digital systems. These devices provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 2.5V, 3V, 3.3V, and 5V powered circuits.These circuits perform a single function: they assert a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 100ms after VCC has risen above the reset threshold. The only difference between the devices is their output. The MAX6326/MAX6346 (push-pull) and MAX6328/MAX6348 (open-drain) have an active-low reset output. The MAX6327/MAX6347 have an active-high push-pull reset output. All of these parts are guaranteed to be in the correct state for VCC down to 1V. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds are factory-trimmable between 2.2V and 4.63V, in approximately 100mV increments. Twenty-one standard versions are available. Contact the factory for availability of nonstandard versions.Ultra-low supply currents (1µA max for the MAX6326/MAX6327/MAX6328) make these parts ideal for use in portable equipment. All six devices are available in space-saving SOT23 and SC70 packages.ApplicationsComputers: Desktop, Workstation, ServerControllersCritical µP and µC Power MonitoringIntelligent InstrumentsPortable Battery-Powered Equipment

The MAX6326/MAX6327/MAX6328/MAX6346/MAX6347/MAX6348 microprocessor (µP) supervisory circuits monitor the power supplies in µP and digital systems. These devices provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 2.5V, 3V, 3.3V, and 5V powered circuits.These circuits perform a single function: they assert a reset signal whenever the VCC supply voltage declines below a preset threshold, keeping it asserted for at least 100ms after VCC has risen above the reset threshold. The only difference between the devices is their output. The MAX6326/MAX6346 (push-pull) and MAX6328/MAX6348 (open-drain) have an active-low reset output. The MAX6327/MAX6347 have an active-high push-pull reset output. All of these parts are guaranteed to be in the correct state for VCC down to 1V. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds are factory-trimmable between 2.2V and 4.63V, in approximately 100mV increments. Twenty-one standard versions are available. Contact the factory for availability of nonstandard versions.Ultra-low supply currents (1µA max for the MAX6326/MAX6327/MAX6328) make these parts ideal for use in portable equipment. All six devices are available in space-saving SOT23 and SC70 packages.ApplicationsComputers: Desktop, Workstation, ServerControllersCritical µP and µC Power MonitoringIntelligent InstrumentsPortable Battery-Powered Equipment

The MAX639/MAX640/MAX653 step-down switching regulators provide high efficiency over a wide range of load currents, delivering up to 225mA. A current-limiting pulse-frequency-modulated (PFM) control scheme gives the devices the benefits of pulse-width-modulated (PWM) converters (high efficiency at heavy loads), while using only 10µA of supply current (vs. 2mA to 10mA for PWM converters). The result is high efficiency over a wide range of loads.The MAX639/MAX640/MAX653 input range is 4V to 11.5V, and the devices provide lower preset output voltages of 5V, 3.3V, and 3V, respectively. Or, the output can be user-adjusted to any voltage from 1.3V to the input voltage.The MAX639/MAX640/MAX653 have an internal 1A power MOSFET switch, making them ideal for minimum-component, low- and medium-power applications. For increased output drive capability, use the MAX649/MAX651/MAX652 step-down controllers, which drive an external P-channel FET to deliver up to 5W.Applications5V to 3.3V Conversion9V Battery to 5V, 3.3V, or 3V ConversionHigh-Efficiency Linear Regulator ReplacementPortable Instruments and Handy-Terminals

The MAX690A/MAX692A/MAX802L/MAX802M/MAX805Lreduce the complexity and number of componentsrequired for power-supply monitoring and battery-controlfunctions in microprocessor (µP) systems. They significantlyimprove system reliability and accuracy comparedto separate ICs or discrete components.These parts provide four functions:1) A reset output during power-up, power-down, andbrownout conditions.2) Battery-backup switching for CMOS RAM, CMOSµP, or other low-power logic.3) A reset pulse if the optional watchdog timer has notbeen toggled within 1.6sec.4) A 1.25V threshold detector for power-fail warning orlow-battery detection, or to monitor a power supplyother than +5V.The parts differ in their reset-voltage threshold levelsand reset outputs. The MAX690A/MAX802L/MAX805Lgenerate a reset pulse when the supply voltage dropsbelow 4.65V, and the MAX692A/MAX802M generate areset below 4.40V. The MAX802L/MAX802M guaranteepower-fail accuracies to ±2%. The MAX805L is thesame as the MAX690A except that RESET is providedinstead of active-low RESET.All parts are available in 8-pin DIP and SO packages.The MAX690A/MAX802L are pin compatible with theMAX690 and MAX694. The MAX692A/MAX802M arepin compatible with the MAX692.ApplicationsBattery-Powered Computers/ControllersCritical µP MonitoringIntelligent Instruments

The MAX705–MAX708/MAX813L microprocessor (µP) supervisory circuits reduce the complexity and number of components required to monitor power-supply and battery functions in µP systems. These devices significantly improve system reliability and accuracy compared to separate ICs or discrete components.The MAX705/MAX706/MAX813L provide four functions:A reset output during power-up, power-down, and brownout conditions.An independent watchdog output that goes low if the watchdog input has not been toggled within 1.6 seconds.A 1.25V threshold detector for power-fail warning, low-battery detection, or for monitoring a power supply other than +5V.An active-low manual-reset input.The MAX707/MAX708 are the same as the MAX705/MAX706, except an active-high reset is substituted for the watchdog timer. The MAX813L is the same as the MAX705, except RESET is provided instead of active-low RESET.Two supply-voltage monitor levels are available: The MAX705/MAX707/MAX813L generate a reset pulse when the supply voltage drops below 4.65V, while the MAX706/MAX708 generate a reset pulse below 4.40V. All four parts are available in 8-pin DIP, SO and µMAX® packages.ApplicationsComputersControllersCritical µP Power MonitoringIntelligent Instruments

The MAX705–MAX708/MAX813L microprocessor (µP) supervisory circuits reduce the complexity and number of components required to monitor power-supply and battery functions in µP systems. These devices significantly improve system reliability and accuracy compared to separate ICs or discrete components.The MAX705/MAX706/MAX813L provide four functions:A reset output during power-up, power-down, and brownout conditions.An independent watchdog output that goes low if the watchdog input has not been toggled within 1.6 seconds.A 1.25V threshold detector for power-fail warning, low-battery detection, or for monitoring a power supply other than +5V.An active-low manual-reset input.The MAX707/MAX708 are the same as the MAX705/MAX706, except an active-high reset is substituted for the watchdog timer. The MAX813L is the same as the MAX705, except RESET is provided instead of active-low RESET.Two supply-voltage monitor levels are available: The MAX705/MAX707/MAX813L generate a reset pulse when the supply voltage drops below 4.65V, while the MAX706/MAX708 generate a reset pulse below 4.40V. All four parts are available in 8-pin DIP, SO and µMAX® packages.ApplicationsComputersControllersCritical µP Power MonitoringIntelligent Instruments

The MAX531/MAX538/MAX539 are low-power, voltage-output, 12-bit digital-to-analog converters (DACs) specified for single +5V power-supply operation. The MAX531 can also be operated with ±5V supplies. The MAX538/MAX539 draw only 140µA, and the MAX531 (with internal reference) draws only 260µA. The MAX538/MAX539 come in 8-pin DIP and SO packages, while the MAX531 comes in 14-pin DIP and SO packages. All parts have been trimmed for offset voltage, gain, and linearity, so no further adjustment is necessary.The MAX538's buffer is fixed at a gain of +1 and the MAX539's buffer at a gain of +2. The MAX531's internal op amp may be configured for a gain of +1 or +2, as well as for unipolar or bipolar output voltages. The MAX531 can also be used as a four-quadrant multiplier without external resistors or op amps.For parallel data inputs, see the MAX530 data sheet.ApplicationsBattery-Operated/Remote Industrial ControlsBattery-Powered Test InstrumentsDigital Gain and Offset ControlGeneral PurposeMachine- and Motion-Control Devices

The MAX548A/MAX549A/MAX550A serial, 8-bit voltage-output digital-to-analog converters (DACs) operate from a single +2.5V to +5.5V supply. Their ±1LSB TUE specification is guaranteed over temperature. Operating current (supply current plus reference current) is typically 75µA per DAC with VDD = 2.5V. In shutdown, the DAC is disconnected from the reference, reducing current drain to less than 1µA. The MAX548A/MAX549A allow each DAC to be shut down independently.The 10MHz, 3-wire serial interface is compatible with SPI™/QSPI™ and Microwire™ interface standards. Double-buffered inputs provide flexibility when updating the DACs; the input and DAC registers can be updated individually or simultaneously.The MAX548A is a dual DAC with an asynchronous load input; it uses VDD as the reference input. The MAX549A is a dual DAC with an external reference input. The MAX550A is a single DAC with an external reference input and an asynchronous load input.The MAX548A/MAX549A/MAX550A's low power consumption and small µMAX® and DIP packages make these devices ideal for portable and battery-powered applications.ApplicationsBattery-Powered ApplicationsComparator-Level SettingsDigital Gain and Offset ControlGaAs Amp Bias ControlGeneral PurposeVCXO Control

The MAX6125/MAX6141/MAX6145/MAX6150/MAX6160 low-dropout, micropower, three-terminal voltage references offer 2.5V, 4.096V, 4.5V, 5.0V, and adjustable (1.23V to 12.4V) output voltages, respectively. Low, 200mV dropout makes these devices ideal for 3V and 5V systems. Unlike two-terminal references that waste battery current and require an external resistor, the MAX61xx family's supply current is virtually independent of input voltage variations, which translates to longer battery life.Initial accuracy for these devices is ±1%. The output temperature coefficient is typically 15ppm/°C, and guaranteed to be less than 50ppm/°C (except for the MAX6160). The MAX6125/MAX6141/MAX6145/MAX6150 are available in 3-pin SOT23 and 8-pin SO packages. The MAX6160 is available in 4-pin SOT143 and 8-pin SO packages.Applications3V/5V SystemsBattery-Powered SystemsData Acquisition SystemsInstrumentation and Process ControlPortable and Handheld Equipment

The MAX6225/MAX6241/MAX6250 are low-noise, precision voltage references with extremely low 1ppm/°C temperature coefficients and excellent ±0.02% initial accuracy. These devices feature buried-zener technology for lowest noise performance. Load-regulation specifications are guaranteed for source and sink currents up to 15mA. Excellent line and load regulation and low output impedance at high frequency make them ideal for high-resolution data-conversion systems up to 16 bits.The MAX6225 is set for 2.500V output, the MAX6241 is set for 4.096V output, and the MAX6250 is set for 5.000V output. All three devices provide for the option of external trimming and noise reduction.ApplicationsA/D ConvertersAutomated Test Equipment (ATE)Digital VoltmetersHigh-Accuracy Industrial and Process ControlHigh-Accuracy Reference StandardHigh-Resolution Analog-to-DigitalPrecision Current Sources

The MAX6301–MAX6304 low-power microprocessor (µP) supervisory circuits provide maximum adjustability for reset and watchdog functions. The reset threshold can be adjusted to any voltage above 1.22V, using external resistors. In addition, the reset and watchdog timeout periods are adjustable using external capacitors. A watchdog select pin extends the watchdog timeout period to 500x. The reset function features immunity to power-supply transients.These four devices differ only in the structure of their reset outputs (see the Selector Guide in the full data sheet). The MAX6301–MAX6304 are available in the space-saving 8-pin µMAX® package, as well as 8-pin PDIP and SO packages.ApplicationsBattery-Powered Computers/ControllersComputers: Desktop, Workstation, ServerCritical µP MonitoringEmbedded ControllersIntelligent InstrumentsMedical EquipmentPortable EquipmentSet-Top Boxes

The MAX6314 low-power CMOS microprocessor (µP) supervisory circuit is designed to monitor power supplies in µP and digital systems. The MAX6314's active-low RESET output is bidirectional, allowing it to be directly connected to µPs with bidirectional reset inputs, such as the 68HC11. It provides excellent circuit reliability and low cost by eliminating external components and adjustments. The MAX6314 also provides a debounced manual reset input.This device performs a single function: it asserts a reset signal whenever the VCC supply voltage falls below a preset threshold or whenever manual reset is asserted. Reset remains asserted for an internally programmed interval (reset timeout period) after VCC has risen above the reset threshold or manual reset is deasserted.The MAX6314 comes with factory-trimmed reset threshold voltages in 100mV increments from 2.5V to 5V. Preset timeout periods of 1ms, 20ms, 140ms, and 1120ms (minimum) are also available. The device comes in a SOT143 package.For a µP supervisor with an open-drain reset pin, see the MAX6315 data sheet.ApplicationsComputers: Desktop, Workstation, ServerControllersCritical µP and µC Power MonitoringIntelligent InstrumentsPortable Battery-Powered Equipment

The MAX5949A/MAX5949B are hot-swap controllers that allow a circuit card to be safely hot plugged into a live backplane. The MAX5949A/MAX5949B operate from -20V to -80V and are well-suited for -48V power systems. These devices are pin and function compatible with the LT4250 and pin compatible with the LT1640.The MAX5949A/MAX5949B provide a controlled turn-on to circuit cards preventing glitches on the power-supply rail and damage to board connectors and components. The MAX5949A/MAX5949B provide undervoltage, overvoltage, and overcurrent protection. These devices ensure the input voltage is stable and within tolerance before applying power to the load.Both the MAX5949A and MAX5949B protect a system against overcurrent and short-circuit conditions by turning off the external MOSFET in the event of a fault condition. The MAX5949A/MAX5949B also provide protection against input voltage steps. During an input voltage step, the MAX5949A/MAX5949B limit the current drawn by the load to a safe level without turning off power to the load.Both devices feature an open-drain power-good status output (PWRGD-bar for the MAX5949A or PWRGD for the MAX5949B) that can be used to enable downstream converters.The MAX5949A/MAX5949B are available in an 8-pin SO package. Both devices are specified for the extended -40°C to +85°C temperature range.Applications-48V Distributed Power SystemsBase-Station Line CardsCentral-Office Line CardsCentral-Office SwitchingNegative Power-Supply ControlsNetwork Routers and SwitchesServer Line CardsTelecom Line Cards

The MAX6173–MAX6177 are low-noise, high-precision voltage references. The devices feature a proprietary temperature-coefficient curvature-correction circuit and laser-trimmed thin-film resistors that result in a very low 3ppm/°C temperature coefficient and excellent ±0.06% initial accuracy. The MAX6173–MAX6177 provide a TEMP output where the output voltage is proportional to the die temperature, making the devices suitable for a wide variety of temperature-sensing applications. The devices also provide a TRIM input, allowing fine trimming of the output voltage with a resistive divider network. Low temperature drift and low noise make the devices ideal for use with high-resolution A/D or D/A converters.The MAX6173–MAX6177 provide accurate preset +2.5V, +3.3V, +4.096V, +5.0V, and +10V reference voltages and accept input voltages up to +40V. The devices draw 320µA (typ) of supply current and source 30mA or sink 2mA of load current. The MAX6173–MAX6177 use bandgap technology for low-noise performance and excellent accuracy. The MAX6173–MAX6177 do not require an output bypass capacitor for stability, and are stable with capacitive loads up to 100µF. Eliminating the output bypass capacitor saves valuable board area in space-critical applications.The MAX6173–MAX6177 are available in an 8-pin SO package and operate over the automotive (-40°C to +125°C) temperature range.ApplicationsADCsAutomotiveDACsDigital VoltmetersThreshold DetectorsVoltage Regulators

The MAX6173–MAX6177 are low-noise, high-precision voltage references. The devices feature a proprietary temperature-coefficient curvature-correction circuit and laser-trimmed thin-film resistors that result in a very low 3ppm/°C temperature coefficient and excellent ±0.06% initial accuracy. The MAX6173–MAX6177 provide a TEMP output where the output voltage is proportional to the die temperature, making the devices suitable for a wide variety of temperature-sensing applications. The devices also provide a TRIM input, allowing fine trimming of the output voltage with a resistive divider network. Low temperature drift and low noise make the devices ideal for use with high-resolution A/D or D/A converters.The MAX6173–MAX6177 provide accurate preset +2.5V, +3.3V, +4.096V, +5.0V, and +10V reference voltages and accept input voltages up to +40V. The devices draw 320µA (typ) of supply current and source 30mA or sink 2mA of load current. The MAX6173–MAX6177 use bandgap technology for low-noise performance and excellent accuracy. The MAX6173–MAX6177 do not require an output bypass capacitor for stability, and are stable with capacitive loads up to 100µF. Eliminating the output bypass capacitor saves valuable board area in space-critical applications.The MAX6173–MAX6177 are available in an 8-pin SO package and operate over the automotive (-40°C to +125°C) temperature range.ApplicationsADCsAutomotiveDACsDigital VoltmetersThreshold DetectorsVoltage Regulators

The MAX6887/MAX6888 multivoltage supply supervisors provide several voltage-detector inputs, one watchdog input, and three outputs. Each voltage-detectorinput offers a factory-set undervoltage and overvoltage threshold. Manual reset and margin disable inputs offer additional flexibility.The MAX6887 offers six voltage-detector inputs, while the MAX6888 offers four inputs. Output active-low RESET asserts when any input voltage drops below its respective undervoltage threshold or manual reset active-low MR is asserted. Output active-low OV asserts when any input voltage exceeds its respective overvoltage threshold. Monitor standard supply voltages listed in the Selector Guide in the full datasheet.The MAX6887/MAX6888 offer a watchdog timer with an initial and normal timeout periods of 102.4s and 1.6s, respectively. Watchdog output active-low WDO asserts when the watchdog timer expires. Connect active-low WDO to manual reset input active-low MR to generate resets when the watchdog timer expires. RESET, OV, and WDO are active-low, open-drain outputs.The MAX6887/MAX6888 are available in a 5mm x 5mm x 0.8mm, 16-pin thin QFN package and operate over the extended -40°C to +85°C temperature range.ApplicationsMultivoltage SystemsNetworkingServers/Workstations/Storage SystemsTelecom

The MAX6966/MAX6967 serial-interfaced peripheralsprovide microprocessors with 10 I/O ports rated to 7V.Each port can be individually configured as either: A 20mA constant-current LED driver (static or pulsewidthmodulated (PWM)). A 10mA constant-current LED driver (static or PWM). An open-drain logic output. An overvoltage-protected Schmitt logic input.Analog and switching LED intensity control is built in: Individual 8-bit PWM control per output. Individual 1-bit analog control (half/full) per output. Global 3-bit analog control applies to all LED outputs.PWM timing of the 10 port outputs may be optionallystaggered, consecutively phased in 45° increments.This spreads the PWM load currents over time in eightsteps, helping to even out the power-supply currentand reduce the RMS current.The MAX6966/MAX6967 can be configured to awakefrom shutdown on receipt of a minimum 3ms pulse onthe active-low CS input. This hardware-wakeup feature allows apower-management controller or similar ASIC to enablethe MAX6966/MAX6967 with preconfigured LED intensitysettings.Shutdown can be programmed to wait up to 4s, fadedown the sink currents to zero for a period of 1/16s to4s, and then shut down. A similar ramp-up from shutdowncan be programmed for 1/16s to 4s.The MAX6966/MAX6967 support hot insertion. All portpins remain high impedance in power-down (V+ = 0V)with up to 8V asserted on them.The DOUT/OSC pin can be configured as either theserial interface data output or optional PWM clockinput. The MAX6966 powers up defaulting as DOUToutput. The MAX6967 defaults as OSC input.For a similar part without the constant-current controls,refer to the MAX7317 data sheet.ApplicationsCell PhonesKeypad BacklightsLCD BacklightsLED Status IndicationPortable EquipmentRGB LED Drivers

The MAX6971 serial-interfaced LED driver provides 16 open-drain, constant-current-sinking LED driver outputs rated at 36V. The MAX6971 operates from a 3V to 5.5V supply. The MAX6971 supply and the LEDs' supply or supplies can power up in any order. The constant-current outputs are programmed together to up to 55mA using a single external resistor. The MAX6971 operates with a 25Mb, industry-standard, 4-wire serial interface.The MAX6971 uses the industry-standard, shift-register-plus-latch-type serial interface. The driver accepts data shifted into a 16-bit shift register using data input DIN and clock input CLK. Input data appears at the DOUT output 16 clock cycles later to allow cascading of multiple MAX6971s. The latch-enable input, LE, loads the 16 bits of shift register data into a 16-bit output latch to set which LEDs are on and which are off. The active-low output-enable, OE, gates all 16 outputs on and off, and is fast enough to be used as a PWM input for LED intensity control.For applications requiring LED fault detection, refer to the MAX6983, which automatically detects open-circuit LEDs.For safety-related applications requiring a watchdog timer, refer to the MAX6983, which includes a fail-safe feature that blanks the display if the serial interface becomes inactive for more than 1s.The MAX6971 is one of a family of 12 shift-register-plus-latch-type LED drivers. The family includes 8-port and 16-port types, with 5.5V- or 36V-rated LED outputs, with and without open-circuit LED detection and watchdog. All versions operate from a 3V to 5.5V supply, and are specified over the -40°C to +125°C temperature range.ApplicationsArchitectural LightingGaming FeaturesMarquee DisplaysPoint-of-Order SignsTraffic SignsVariable Message Signs

The MAX6979 serial-interfaced LED driver provides 16open-drain, constant-current-sinking LED driver outputsrated at 5.5V. The MAX6979 operates from a 3V to 5.5Vsupply. The MAX6979 supply and the LEDs' supply canpower up in any order. The constant-current outputsare programmed together to up to 55mA using a singleexternal resistor. The MAX6979 operates with a 25Mb,industry-standard, 4-wire serial interface.The MAX6979 includes circuitry that automaticallydetects open-circuit LEDs. Fault status is loaded into theserial-interface shift register when LE goes high and isautomatically shifted out on DOUT when the next datatransmission is shifted in.The MAX6979 includes a fail-safe feature for safety-relatedapplications, which blanks the display if the serialinterface fails. If the serial interface becomesinactive for more than 1s, all driver output latches areautomatically cleared. This turns off all LEDs connectedto the outputs. The shift register data is not disturbed.The outputs remain off until the driver output latches areupdated with data turning them on, so recovery is automaticif the transmission failure is temporary. Thewatchdog function requires no software change to theapplication driving the MAX6979.The MAX6979 uses the industry-standard shift-register-plus-latch-type serial interface. The driver accepts datashifted into a 16-bit shift register using data input DINand clock input CLK. Input data appears at the outputDOUT 16 clock cycles later to allow cascading of multipleMAX6979s. The latch-enable input, LE, loads the 16bits of shift-register data into a 16-bit output latch to setwhich LEDs are on and which are off. The output-enableinput, OE-bar, gates all 16 outputs on and off, and isfast enough to be used as a PWM input for LED intensitycontrol.The MAX6979 is one of a family of 12 shift-register-plus-latch-type LED drivers. The family includes 8-port and16-port types, with 5.5V- or 36V-rated LED outputs, withand without open-circuit LED detection and watchdog.All versions operate from a 3V to 5.5V supply, and arespecified over the -40°C to +125°C temperature range.ApplicationsArchitectural LightingGaming FeaturesMarquee DisplaysPoint-of-Order SignsTraffic SignsVariable Message Signs