MicroLogix 1500

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The Allen-Bradley MicroLogix 1500 Programmable Logic Controllers are modularly designed with many components that can be changed to accommodate different application needs in terms of power type and processor capabilities, as well as several components that can be easily added to the devices to increase their scope. The basic elements used to configure these PLCs are base units that include 120 to 240 Volts AC or 24 Volts DC power supplies and 24 or 28 I/Os and processors. When the desired categories of these 2 types of components are selected and physically connected, the devices become fully functional and the items visible on the units are removable terminal blocks, interfaces to expansion modules (hidden behind the plate), groups of input and output status LEDs, device status LEDs, communication ports, batteries, mode switches, and trim potentiometers. Other parts that can be additionally mounted are a memory module, a replacement battery, and a data access tool.


The programming of the Allen-Bradley MicroLogix 1500 small programmable logic controllers is done by using the RSLogix 500 software when the controllers are connected to personal computers. The Allen-Bradley 1769 compact expansion I/O modules can be attached to the device to expand its I/O capabilities. The digital input circuit types on the MicroLogix 1500 devices are 24 Volts DC sink/source or 120 Volts AC inputs, and the digital output circuit types are relays or combinations of relays and FET transistors. To determine the current status of the PLCs, the users have 8 status LEDs which are the power, run, fault, force, battery-low, COMM 0, COMM 1, and DCOMM LEDs. The operating system of the units can be upgraded with a newer one in the controlFLASH upgrade kit.

Allen-Bradley 1764 MicroLogix 1500 Controllers

Technical Specifications 

  • 1764 MicroLogix 1500 Controllers input-voltage range from 120V AC or 24V DC
  • RS-232 communication port supports:
    • DF1 full-duplex
    • DF1 half-duplex slave
    • DH1 half-duplex master
    • Modbus RTU slave
    • Modbus RTU master
    • DH-485
    • ASCII
  • Panel or DIN-rail mounting 
  • Standard and enhanced processor options available 
  • Optional RTC (real-time clock) and Memory Modules options 

Allen-Bradley 1764 MicroLogix 1500 Controllers

Technical Specifications 

  • 1764 MicroLogix 1500 Controllers input-voltage range from 120V AC or 24V DC
  • RS-232 communication port supports:
    • DF1 full-duplex
    • DF1 half-duplex slave
    • DH1 half-duplex master
    • Modbus RTU slave
    • Modbus RTU master
    • DH-485
    • ASCII
  • Panel or DIN-rail mounting 
  • Standard and enhanced processor options available 
  • Optional RTC (real-time clock) and Memory Modules options 

Troubleshooting Your MicroLogix 1500 Controller

This section describes how to troubleshoot your MicroLogix 1500 controller. This section will cover the process of understanding your controller LED status, a controller error recovery schematic, and identifying controller faults. 

Understanding MicroLogix 1500 Controller LEDs

The controller status LEDs provide a way to determine the current status of the controller if a programming device is not present, available, or connected. 

LED Color Indicates
POWER Off No input power
Green Power on
RUN Off  MicroLogix 1500 controller is not in Run mode or REM Run
Green Controller is in Run mode or REM Run
Green Flashing System is not in Run mode. Memory module transfer is in process. 
FAULT Off No fault detected
Red Flashing Faulted user program
Red Processor hardware fault or critical fault
FORCE Off No forces installed
Amber Forces installed
BATTERY LOW  Off Battery OK
Red Battery needs replacement
COMM 0  Off Flashes when communications are active
Green  
COMM 1 (1764-LRP only) Off Flashes when communications are active
Green  
DCOMM*** Off User configured communications mode is active
Green Default communications mode active
INPUTS Off Input is not energized
Green Input is energized (logic status)
OUTPUTS Off Output is not energized
Amber Output is energized. 

***When using a 1764-LRP processor, the DCOMM LED applies only to Channel 0. 

When Operating Normally

The POWER and RUN LEDs are on. If a force condition is present, the FORCE LED turns on and remains on until all forces are removed. 

When An Error Exists

 

If the LEDs Indicate The Following Error Exists Probable Cause Recommended Action To Solve
All LEDs off No input power or power supply error No line power Verify proper line voltage and connections to the controller.
Power supply overload This problem may occur intermittently if the power supply is overloaded when output loading and temperature varies. 
Power and FAULT LEDs on solid Hardware faulted Processor Hardware Error Cycle power.  
Loose wiring Inspect connections to controller to ensure that they are connected. 
Power LED on and FAULT LED flashing Application fault Hardware/Software Major Fault Detected

1. Monitor Status File Word S:6 for major error code.

2. Remove hardware/software condition causing fault. 

3. Clear Major Error Halted flag, bit S2:1/13

Attempt a MicroLogix 1500 controller Run mode entry. If unsuccessful, repeat recommended action steps above.

Controller Error Recovery Schematic

Use the error recovery schematic below to help you diagnose software and hardware problems in the micro controller. The model provides common questions you might ask to help troubleshoot your system. Refer to the recommended pages within the model for further help. 

  1. Is the error hardware related?
    1. If NO: (1) Identify the error code and description, (2) Refer to "When An Error Occurs" table (above) for probable cause and recommended action, (3) Clear the Fault, (4) Correct the condition causing the fault, (5) Return controller to RUN or any of the REM test modes, and (FTest and verify system operation
    2. If YES: Are the wire connections tight?
      1. If NO: (1) Tighten wire connections, and (F). 
      2. If YES: Is the Power LED on? 
        1. If NO: Is power supplied to the controller?
          1. If YES: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 
          2. If NO: (1) Check power, and (F). 
        2. If YES: Is the RUN LED on?
          1. If YES: (F). 
          2. If NO: Is the Fault LED on?
            1. If YES: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 
            2. If NO: Is an input LED accurately showing status? 
              1. If Yes: (F). 
              2. If NO: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 

Identifying Controller Faults

While a program is executing, a fault may occur within the operating system or your program. When a fault occurs, you have several options to determine what the fault is and how to correct it. 

Automatically Clearing Faults

You can automatically clear a fault by cycling power to the MicroLogix 1500 controller when the Fault Override at Power-up bit (S:1/8) is set in the status file. You can also configure the controller to clear faults and go to RUN every time the controller is power cycled. This is a feature that OEMs can build into their equipment to allow end users to reset the controller. If the controller faults it can be reset by simply cycling power to the machine. To accomplish this, set the following bits in the status file: 

  • S2:1/8 - Fault Override at Power-Up
  • S2:1/12 - Mode Behavior

If the fault condition still occurs after cycling power, the controller reenters the fault mode. 

Manually Clearing Faults Using the Fault Routine

The occurrence of recoverable or non-recoverable user faults can cause the user fault subroutine to be executed. If the fault is recoverable, the subroutine can be used to correct the problem and clear the fault bit S:1/13. The controller then continues in the Run or test mode. The subroutine does not execute for non-user faults. Refer to the MicroLogix 1200 and MicroLogix 1500 Instruction Set Reference Manual publication 1762-RM001 for information on creating a user fault subroutine. 

MicroLogix 1500 Controller Repairs

Here at DO Supply, we offer repair services for your Allen-Bradley products, such as the Allen-Bradley MicroLogix 1500 Controller. Please select the Repairs tab for more information or to request a quote. 

MicroLogix 1500 Description Stock Level
1764-24AWAAllen-Bradley MicroLogix 1500 with I/O Rating, 120 Volts AC and 512 Max IO Expansion
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1764-24BWAAllen-Bradley MicroLogix 1500 with I/O Rating, 24 Volts DC and 512 Max IO Expansion
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1764-28BXBAllen-Bradley MicroLogix 1500 with I/O Rating, 24 Volts DC and 512 Max IO Expansion
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1764-DATAllen-Bradley MicroLogix 1500 with Data Access Tool function, Display Screen feature, and 512 Max IO Expansion
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1764-LRPAllen-Bradley MicroLogix 1500 with Processor Unit function, 14 Kb memory, and DH-485, Modbus, DF1, and ACSII communication
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1764-LSPAllen-Bradley MicroLogix 1500 with Processor Unit function, 7.6 Kb memory, and DH-485, Modbus, DF1, and ACSII communicatio...
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1764-MM1Allen-Bradley MicroLogix 1500 with Memory Module function, 8 Kb memory, and DH-485, Modbus, DF1, and ACSII communication
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1764-MM1RTCAllen-Bradley MicroLogix 1500 with Memory Module with RTC function, 8 Kb memory, and Real-Time Clock communication
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1764-MM2Allen-Bradley MicroLogix 1500 with Memory Module function, 16 Kb memory, and Real-Time Clock communication
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1764-MM2RTCAllen-Bradley MicroLogix 1500 with Memory Module with RTC function, 16 Kb memory, and Real-Time Clock communication
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1764-MM3Allen-Bradley MicroLogix 1500 with Memory Module function, 64 Kb memory, and Real-Time Clock communication
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1764-MM3RTCAllen-Bradley MicroLogix 1500 with Memory Module with RTC function, 64 Kb memory, and Real-Time Clock communication
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1764-RTCAllen-Bradley MicroLogix 1500 RTC Module with Real-Time Clock and IP20 enclosure
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MicroLogix 1500 Description Stock Level