External Brown-out Protection for C51 Microcontrollers with Active High Reset Input Features • • • • • • • Low-voltage Detector Prevents Register and EEPROM/Flash Corruption One Discrete Solution Integrated IC Solution Low-power/Low-cost Solution Formulas for Component Value Calculations Complete with Sample Schematics C51 Microcontrollers Application Note Introduction This application note shows in detail how to prevent system malfunction during periods of insufficient power supply voltage. It describes techniques to prevent the MCU from executing code during periods of insufficient voltage by using external low voltage detectors. These events are often referred to as “Brown-outs”, where power supply voltage drops to an insufficient level, or “Black-outs” where power supply voltage totally disappear for a period of time. One discrete solution is discussed in detail, allowing the user to calibrate the system requirements. A complete guide to Integrated Circuit (IC) solutions is also included. By implementing these techniques, the following can be prevented: • MCU Register Corruption • I/O Register Corruption • I/O-pin Random Toggling • On-chip Memory Corruption (SRAM, EEPROM, Flash) • External Memory Corruption Rev. 4183A–80C51–11/02 1 RST Pin Description A high on the RST pin for several machine cycles while the oscillator is running, resets the device. An internal resistor to VSS permits a power-on reset using only an external capacitor to VCC. While this pin is forced high, the MCU Core is halted from executing code, the peripherals are stopped and the I/Os are tri-stated. The RST pin is an output when the Hardware Watchdog Timer times out and forces a system reset. When Watchdog Timer overflows, it drives an output RST HIGH pulse at the RST pin. When the watchdog is used, a resistor Rrst mounted in serial with the external capacitor Crst or reset circuit is necessary to allow the Hardware Watchdog to drive the RST pin. Theory of Operation For the MCU to successfully decode and execute instructions, the supplied voltage must always stay above the minimum voltage level specified by the product datasheet. When supplied voltage drops below this level, the MCU might to execute some instructions incorrectly. The result is unexpected activity on the internal data and control lines. This activity may cause MCU Registers, I/O Registers and Data Memories to get corrupted. To avoid unexpected activity, the MCU should be prevented from executing code during periods of insufficient supply voltage. This is best ensured by using a Power Supply Low Voltage Detector. Below a fixed threshold voltage VT, the detector circuit forces the RST pin high (active). Forcing RST high immediately stops the MCU from executing code. While the supplied voltage is below the required threshold voltage VT , the MCU is halted, making sure the system stays in a known state. When the supplied voltage rises above this predefined voltage, the RST pin is again released, and the MCU starts to execute code beginning at the Reset Vector. Preventing SFR Corruption When the Detector keeps the MCU in Reset, all MCU activity is halted. When released from Reset, all the Special Function Registers (SFRs) are in their default state. Without a Detector, random MCU activity such as described before might cause the Special Function Registers to get corrupted. See “Volatile Memory” below. Preventing I/O Register Corruption When using a Detector to keep the MCU in Reset, all I/O Registers are kept in their default state for the duration of the reset. Consequently, all on-chip peripherals will stay in their reset state. Without a Detector, random MCU activity such as described before might write an unknown value to any I/O Register. This may cause unexpected behavior of the on-chip peripherals. Preventing I/O Pin Random Toggling A Detector will keep the MCU in Reset, and all I/O pins are kept in their default state for the duration of the Reset. Without a Detector, random MCU activity such as described before might write a random value to the I/O Registers. This may cause random toggling of the I/O pins. Preventing Volatile Onchip Memory Corruption Using a Detector to keep the MCU in Reset, there will be no access to the volatile onchip memory. The memory will keep its present content for the duration of the Reset. Without a Detector, random MCU activity such as described in the introduction may write an unknown value to any volatile on-chip memory location. 2 C51 MCUs 4183A–80C51–11/02 C51 MCUs Preventing External Components Corruption Using a Detector to keep the MCU in Reset, prevents access to the external components such as memories, peripherals, latches, etc. These components will keep their contents or status for the duration of the Reset. Without a Detector, random MCU activity could write an unknown value to any External Components address (SRAM locations, peripheral command registers, etc.). Preventing Non volatile On-chip Memory Corruption Non volatile memories such as EEPROM, and Flash are designed to keep their contents even when power is completely removed from the system. By the use of a Detector to keep the MCU in Reset, activity on the control lines ceases. The memory contents are then prevented from unintentional writes from the MCU for the duration of the Reset. Without a Detector, random MCU activity could initialize an unintended write to the nonvolatile memory. This may cause random corruption of the memory contents. Since the C51 MCU is capable of writing to its own program memory, the internal Flash Program memory contents could be affected by a power failure situation. Notes: 1. For any write to non volatile memory, a minimum voltage is required to successfully write the new values into the memory. If supplied voltage at any time during the write cycle drops below the minimum voltage, the write might fail, corrupting the location written to. 2. When the reset activates during a write to the internal EEPROM, the operation is aborted. The result can be seen when the location being written get corrupted. Design Criteria Threshold Voltage It is recommended to set the threshold voltage below minimum VCC to allow for small fluctuations in supplied voltage (VTMAX must be less than “Supply Voltage Min”). The threshold voltage should always be selected to ensure that the Detector keeps the device properly reset when supply voltage drops below the critical voltage required by the MCU (VTMIN must be greater than “Component Specification VCC Min”). Care should be taken to ensure sufficiently high detector threshold voltage even in worst case situations. See Table 4 on page 14 for examples. Figure 1. Threshold Voltage Choice Component Specification Supply Voltage Treshold Voltage Hysteresis VccMAX VccMAX VccMIN VTMAX HIGH LOW VTMIN VccMIN 3 4183A–80C51–11/02 Hysteresis Hysteresis is the difference in the voltage between the positive-going switching threshold and the negative-going switching threshold. Without hysteresis, it is possible that system or environmental noise could cause a rising signal to toggle from low to high, then high to low again in immediate succession. Hysteresis must ensure that any noise on the VCC input is unable to cause a rising RST signal to toggle once it has gone from low to high or a falling RST signal to toggle once it has gone from high to low. Typical values for hysteresis are 0.2 - 0.3V, it must be selected according to VCC characteristics. The hysteresis thresholds must be contained between VTMIN and VTMAX. Operating Voltage Range Carefully monitor the MCU since it can operate with a supply voltage below its Vcc min. However, its behavior may be erratic. The MCU oscillator can run with a supply voltage near 1 volt. Under these conditions, the Brown-out circuit must generate a valid RST signal. Output Transition Delay 4 Output transition (propagation delay and slew rate) must be fast enough to stop the MCU before it causes memory corruption or unexpected behavior of peripherals. C51 MCUs 4183A–80C51–11/02 C51 MCUs Implementation Design Hint: Supply Voltage Filtering, Oscillator Stability A variety of Integrated Circuit (IC) solutions are available from different manufacturers. These solutions offer high accuracy at a low price, typically they guarantee the threshold voltage to be within ± 1%. Although the elementary three-pin fixed voltage detector is available, there is also a whole range of devices offering additional features such as Reset Pulse stretching, Power-on Reset Time-out, Watchdogs, Power regulation, dual supply switching for uninterruptible Power Supply operation and more. Included in this application note is a guide to integrated circuit solutions available. As an alternative, this application note also presents one discrete Low-power Supply Voltage RESET Detector. • Alternative 1: Minimum Power Consumption. Well-suited for battery-powered applications where power consumption is the most critical parameter. • Alternative 2: High accuracy, low-power consumption using commercial semiconductor ICs. Use low impedance capacitors (low ESR and ESL) on the VCC and multi-layer PCB with power planes to improve transient rejection from the power supply. To provide good MCU startup, the oscillator must be stable for several cycles before releasing the RST signal (refer to the device documentation). 5 4183A–80C51–11/02 Alternative 1: Lowpower Consumption Characteristics • • • • • • • Very Low-power Consumption, (Typ 0.5 µA@3V, 1 µA@5V) Low-cost Solution Large Hysteresis, Typ. 0.3 Volts Fast Output Transitions Accuracy ± 5 - 10% High Component Count Long Response Time against VCC Figure 2. Low-power Consumption Brown-out Detector (1) (2) Vcc OPTIONAL RESET SWITCH VCCOPTIONAL Optional Vcc RESET Switch SWITCH Reset R2 C1 C2 + R2 C51 MCU Crst 1µF + T1 T1 T2 R3 R1 Rrst 1K T2 T3 R3 C3 C3 R1 C2 R4 R5 R4 Notes: C51MCU MCU C51 (2) Vcc HWDT Rrst RST 1-5K HWDT (1) R RST 50-200K T3 C1 Vcc Crst 1µF Vss R5 R 50-200K Vss 1. Refer to the component specifications, some products such as T89C51CC02 have an extended tolerance range from 20K to 200K. 2. HWDT: Hardware Watchdog Timer Figure 3. Oscilloscope Plots Show how the Voltage on RST Varies with VCC 3V Vcc Vcc RST RST 6 C51 MCUs 4183A–80C51–11/02 C51 MCUs Introduction The circuit shown in Figure 2 on page 6 benefits from low-power consumption, which makes it suitable for battery operated applications. Standard discrete components provide a low cost design. The voltage transition on the RST pin is very steep. Combined with the large hysteresis, the accuracy is high. However, the response time is slow, which makes it unsuitable for rapidly varying supply voltages. Theory of Operation The Brown-out Detector has two stages, the Detector and the Amplifier. In the Detector stage, the threshold voltage is set by the resistors R1 and R2 in relation to the critical voltage of transistor T1. Under normal operation, this transistor is conducting. When the supply voltage drops below the threshold voltage, the transistor shuts off. The output from this Detector leads to the input of the ultra low power Amplifier stage. Under normal operation, the low voltage of the base of transistor T2 causes it to remain shut, allowing resistor R5 to pull the RST input low. The Amplifier stage also contains a hysteresis feedback loop through transistor T3, short-circuiting a resistor R3 in the amplifier when the RST output is kept high. Selecting Components T1, T2, and T3 The production spread of current gain β (or hFE) in transistor T1 affects the threshold voltage VT (typically ± 0.2 volts). Most small signal transistors can be used, but low production spread transistors are recommended. CAUTION: If transistor T1 is changed from one type to another. The emitter-base threshold voltage of T1 affects the constant (VBE) in the equation for threshold voltage (below). As a consequence, a change of transistor could cause a change in the threshold voltage of the detector, which requires the voltage divider R1 + R2 to be recalculated. R1 and R2 R1 and R2 form a voltage divider that defines the threshold voltage VT. As the threshold voltage depends on these resistors, it is recommended to choose resistors with 1% tolerance or better. See “Noise Sensitivity”. R1 is usually chosen equal to 10 MΩ to ensure the lowest power consumption possible. R2 is then found by the equation below. The constant (Vbe) in the equation may vary slightly with variations in transistor T1: Vbe Vbe ⋅ R1 V T = ( R1 + R2 ) ⋅ ----------- , or R2 = ----------------------- R2 V T – Vbe Note: Vbe is the T1 base to supply voltage and typically it equals 0.4V to 0.6V. R3 R3 is a non-critical pull-up resistor that has very little influence on the threshold voltage. It should be selected as large as possible to minimize power consumption. A resistance of R3 greater than 10 MΩ is not recommended, see “Noise Sensitivity” below. R4 Resistor R4 defines the hysteresis of the threshold voltage (VT). By choosing R4 to 3.3 MΩ, the resulting hysteresis will be approximately 0.3 volts. A smaller R4 will give a larger hysteresis, a larger R4 gives smaller hysteresis. A larger R4 will also result in a less sharp transition in the output slope of the RST signal. Large deviations from the recommended value will eventually alter the constant VBE in the threshold voltage equation above. As the hysteresis is only slightly changed with variation in R4 resistance, the accuracy is not critical. 7 4183A–80C51–11/02 R5 Resistor R5 pulls the RST pin low in normal operating mode. A value in the range of 100 kΩ is recommended to tie RST securely to GND. As no current goes through this resistor in normal operating mode, its value and accuracy is of little importance. When RST is pulled high, this resistor will start conducting a relatively large current. C1 and C2 Capacitors C1 and C2 reduce RF noise picked up in the circuitry and amplified by the transistors. Both capacitors can be omitted, but a value greater than 1 nF is recommended. For maximum noise immunity, 100 nF (LF) or capacitors with lower ESR (HF) should be selected when possible. Also see “Response Time” below. The accuracy is not critical, but to ensure proper RF decoupling, the capacitors should have Z5U dielectric or better. C3 Capacitor C3 decouples the power lines. It can be omitted if there is RF decoupling of the power lines somewhere nearby on the circuit board, otherwise 1 nF is recommended. For maximum noise immunity, 100 nF (LF) or low ESR (HF) should be selected. Crst Capacitor Crst (typically 1 µF) from the RST pin to the VCC supply rail is the simplest way to achieve a reset time of approximatively 100 msS. This reset time is dependant on the sink current defined by the microcontroller (refer to the device specification). Crst must be selected to ensure that the RST signal is high during at least two machine cycles after the power on (refer to the device specification). Rrst Rrst is necessary when the Hardware Watchdog of the MCU is used. It allows the MCU to drive the RST pin high and it limits the output current of the RST pin. The recommended value is 1 to 5K. Reset Switch/In-System Programming If a push button reset is required, it is simply connected in parallel as shown in Figure 2. As the switch/programmer will pull RST high, power consumption in R5 will be relatively high for the duration of the event. Also see “Power Consumption”. Response Time Choosing large values for capacitors C1 and C2 will slow down the circuit’s response time. This is not a problem with battery driven applications where the supply voltage decreases slowly over time. Allthough the response time also applies to the time immediately following power-on. This could affect operation when a flat battery is loaded. When power can drop more rapidly, the long response time due to C1 and C2 should be taken into consideration. Noise Sensitivity Choosing values of R1 and R3 greater than 10 MΩ is not recommended, as it makes the circuitry sensitive to thermal noise generated in the resistor. When noise is not critical, the values of R1 and R3 can be raised to 20 MΩ. Choosing larger values will result in the resistors not conducting sufficient current, giving in a non-functional Detector. If more noise immunity is required, these resistors can be reduced with smaller ones, at the expense of increased power consumption. Capacitors C1, C2 and C3 are decoupling capacitors to minimize noise sensitivity to both RF and 50/60 Hz fields. They can all be omitted, but the noise immunity greatly depends on the values selected. 8 C51 MCUs 4183A–80C51–11/02 C51 MCUs Threshold Accuracy Because the threshold voltage is defined mainly by R1 and R2, inaccuracies in these resistors directly influence the threshold voltage accuracy. It is recommended to choose these with ± 1% tolerance. Power Consumption The current consumption in normal operating mode (sufficiently high VCC) is found by: V CC 1 1 I ≈ ---------------------------------------------------------- = V CC --------------------- + --------------------- ( R1 + R2 ) || ( R3 + R4 ) R1 + R2 R3 + R4 When reset switch or programmer force RST to GND, the current increases to: V CC I ≈ ------------------------------------------------------------------------------------------------|| ( R1 + R2 ) ( R3 + R4 ) || R5 || R RESET When voltage drops to the level where the detector activates, transistor T1 closes, T2 opens and the current is: V CC I ≈ ----------------------------------------------------------------( R1 + R2 ) || R5 || R RESET As resistor R5 is usually chosen much smaller than the other resistors R1-R4, the last two expressions both simplify to: V CC I ≈ --------------------------------R5 || R RESET Note: The operator indicates resistors are parallel. Table 1. Example Values when MCU RST Internal Pull-down is in the Range 50 - 200K Example Values Component 3.0V 4.5V Recommended Tolerance T1, T2 BC558/BC888/2N3906 ICE ≥ 2.5 mA, VCE ≥ 8 V, β/hFE ≥ 100 T3 BC548/BC848/2N3904 ICE ≥ 2.5 mA, VCE ≥ 8 V, β/hFE ≥ 100 R1 10 MΩ ≤ 1% R2 1.54 MΩ 976 kΩ ≤ 1% R3 6.8 MΩ ≤ 20% R4 3.3 MΩ ≤ 20% R5 100 kΩ ≤ 20% C1, C2, C3 100 nF ≤ 20%, Z5U dielectric or better In Table 1 the values are calculated to minimize the power consumption. 9 4183A–80C51–11/02 In Table 2 the transistor T2 can source more current. The Vbe constant is approximately 0.5V. Table 2. Example Values when MCU RST Internal Pull-down is in the Range 20 - 200K Example Values Component 10 3.0V 4.5V Recommended Tolerance T1, T2 BC558/BC888/2N3906 ICE ≥ 2.5 mA, VCE ≥ 8 V, β/hFE ≥ 100 T3 BC548/BC848/2N3904 ICE ≥ 2.5 mA, VCE ≥ 8 V, β/hFE ≥ 100 R1 6.04 MΩ 6.19 MΩ ≤ 1% R2 1.3 MΩ 820 kΩ ≤ 1% R3 1.5 MΩ ≤ 20% R4 510 KΩ ≤ 20% R5 100 kΩ ≤ 20% C1, C2, C3 100 nF ≤ 20%, Z5U dielectric or better C51 MCUs 4183A–80C51–11/02 C51 MCUs Alternative 2: Integrated Circuit Solutions Characteristics • • • • • • Introduction A selection of integrated circuits is available from various semiconductor suppliers. They vary from simple 3-pin fixed voltage detectors to advanced circuitry containing Watchdog Timers and Power-on Reset (POR) Time-outs. Because some C51 MCUs have built-in Watchdog and POR circuitry, these functions do not need to be handled by the external IC. The threshold accuracy is better than ± 1% for most circuits. Current consumption is in the µA range. Make sure to choose a device with an active high output. A wide variety of package types are available, ranging from miniature 3-pin SOT-23 to large packages with high-pin count. Easy to Mount Very Accurate Threshold Voltage Low Power Consumption Small Footprint Low Component Count Wide Variety of Additional Functionality Figure 4. Detector with Push-pull Output Vcc Detector DETECTOR Logic Rrst 1-5K RST LOGIC Output Driver Generally, a standard IC has push-pull Reset output, either CMOS or TTL output levels. A manual reset button can be implemented with this type of output, with the addition of a resistor in series with the output. The manual button is connected between the resistor Rrst and the RST pin (see Figure 4). This resistor is also necessary when the Hardware Watchdog of the MCU is used. An alternate location for the reset button is given on Figure 5. 11 4183A–80C51–11/02 Figure 5. Optional Location of Manual Reset Switch Vcc MR/ Rrst 1-5K Detector DETECTOR Logic LOGIC RST Reset RESET Switch SWITCH Reset Pulse Stretching An additional feature in some of these circuits is stretching of the reset pulse. The Reset is held active for a defined amount of time after the condition (Power-on Reset, Brownout Reset, etc.) that caused the reset has disappeared (see Figure 6). Some of these devices also provide this feature for the Manual Reset. The device senses the output level, detects the closing and opening of a reset button. When the button is released, the device keeps the RST line active for an additional amount of time. Figure 6. Reset Pulse Stretching Vcc VT tBROWN-OUT tRST RST Power Regulator Several integrated power regulators include the Low-voltage Detector, combining both functionalities in one device. This reduces part count, and often adds the functionality at no extra cost. Battery Backup Solutions Some systems contain a battery to supply power when the main power drops. The power regulator in such systems often provides a status signal to the MCU telling which source currently supplies power to the circuit. Connecting this signal to an input pin, the C51 MCU can detect the event and execute a safe power-down sequence, switching off power hungry peripheral equipment (motor, display etc.) before entering Power-down mode. When main power supply voltage returns to an acceptable level, the C51 MCU should detect the event, wake up and resume execution where it left off. 12 C51 MCUs 4183A–80C51–11/02 C51 MCUs Hysteresis Hysteresis in the Low-voltage Detector might be implemented in the integrated circuit, or can be added with external circuitry (Figure 7). This prevents the detector from oscillating when used in battery applications. Figure 7. Adding Hysteresis to Threshold Voltage Vcc R1 R2 Rrst 1-5K Detector DETECTOR LOGIC Logic Fixed/Adjustable Threshold Voltage RST Some circuits offer the threshold voltage VT to be tuned by external components, while others have a preset threshold voltage reference. The use of a fixed threshold voltage IC is shown in Figure 8. The typical connection for externally tuned threshold voltage is shown in Figure 8. This device offers an internal voltage reference and a comparator. If the voltage at the input pin is higher than the reference voltage, the output will be activated. The threshold voltage is easily defined by a voltage divider, R1 and R2. Figure 8. Integrated Reset Circuit with Preset Threshold Voltage Vcc R1 Vcc IN R2 Operating Voltage Rrst 1K RST RESET GND The Brown-out device should guarantee the generation of an active RST signal when the supply voltage is out of the operating voltage range of the MCU and while an activity of the MCU is possible. See “Operating Voltage Range” on page 4. 13 4183A–80C51–11/02 Table 3. Example of Integrated Circuit Devices Device Features MAX810/LM810/ADM810 MAX812 (1) Fixed Threshold Voltage, Adjustable Pulse Stretching, Low Power (2) Fixed Threshold Voltage, Fixed Pulse Stretching DS1813/18 V6301 (2) (3) 1. 2. 3. 4. Fixed Threshold Voltage, Fixed Pulse Stretching, Feedback Monitor Fixed Threshold Voltage, Fixed Pulse Stretching, Low Power TLC7703/33/05(4) Notes: Fixed Threshold Voltage, Fixed Pulse Stretching Fixed Threshold Voltage, Fixed Pulse Stretching, Low Power, Manual Reset Input MAX822(1) DS1812 (1) Fixed Threshold Voltage, Ajustable Pulse Stretching Maxim Integrated Product, Inc./ON Semiconductors/National Semiconductor/Analog Devices Dallas Semiconductors. EM Microelectronic-Marin SA. Texas Instruments Table 4. Threshold Voltage Example Values Component Component Nominal Specifications Power Supply Regulator Examples 3.3V VOUTMIN : 3.235V LM1086-3.3 : AT89C51RB2/RC2-M VOUTMAX : 3.365V VCCMIN : 2.7V VCCMAX : 5.5V MC7805 : 5V VOUTMIN : 4.75V VOUTMAX : 5.25V MC7805 : T89C51RD2-M VCCMIN : 3V VCCMAX : 5.5V 5V VCCMIN : 2.7V VCCMAX : 3.6V 3.3V VOUTMIN : 4.75V VOUTMAX : 5.25V LM1086-3.3 : T89C51RD2-L VOUTMIN : 3.235V VOUTMAX : 3.365V LM1086-3.3 : 3.3V T89C51CC01 T89C51CC02 VOUTMIN : 3.235V VOUTMAX : 3.365V VCCMIN : 3V VCCMAX : 5.5V MC7805 : 5V VOUTMIN : 4.75V VOUTMAX : 5.25V 14 Threshold Voltage Range Possibilities VTMAX > 2.7V VTMAX < 3.235V VTMAX > 4.5V VTMAX < 4.75V VTMAX > 3V VTMAX < 4.75V VTMAX > 2.7V VTMAX < 3.235V VTMAX > 3V VTMAX < 3.235V VTMAX > 3V VTMAX < 4.75V Brown-Out IC Example ADM810T VTMAX = 3V VTMAX = 3.15V ADM810L VTMAX = 4.5V VTMAX = 4.75V ADM810M VTMAX = 4.25V VTMAX = 4.5V ADM810T VTMAX = 3V VTMAX = 3.15V ADM810T VTMAX = 3V VTMAX = 3.15V ADM810M VTMAX = 4.25V VTMAX = 4.5V C51 MCUs 4183A–80C51–11/02 Atmel Headquarters Atmel Operations Corporate Headquarters Memory 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 487-2600 Europe Atmel Sarl Route des Arsenaux 41 Case Postale 80 CH-1705 Fribourg Switzerland TEL (41) 26-426-5555 FAX (41) 26-426-5500 Asia Room 1219 Chinachem Golden Plaza 77 Mody Road Tsimhatsui East Kowloon Hong Kong TEL (852) 2721-9778 FAX (852) 2722-1369 Japan 9F, Tonetsu Shinkawa Bldg. 1-24-8 Shinkawa Chuo-ku, Tokyo 104-0033 Japan TEL (81) 3-3523-3551 FAX (81) 3-3523-7581 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 436-4314 RF/Automotive Theresienstrasse 2 Postfach 3535 74025 Heilbronn, Germany TEL (49) 71-31-67-0 FAX (49) 71-31-67-2340 Microcontrollers 2325 Orchard Parkway San Jose, CA 95131 TEL 1(408) 441-0311 FAX 1(408) 436-4314 La Chantrerie BP 70602 44306 Nantes Cedex 3, France TEL (33) 2-40-18-18-18 FAX (33) 2-40-18-19-60 ASIC/ASSP/Smart Cards 1150 East Cheyenne Mtn. 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