Allen Bradley PLC Programming Guide, How to Program an Allen Bradley PLC?

1. Preparation for programming

1.1. Choose the right programming device

When programming Allen Bradley PLC, it is very important to choose the right programming device. Usually, the computer is the most commonly used programming device. There are many ways to connect the computer to the PLC, among which serial port connection and USB connection are more common.
For serial port connection, depending on the AB PLC model, you can choose to use RS232 or USB interface for connection. The RS232 interface requires a 9-pin or 25-pin serial cable, while the USB interface requires a corresponding USB-to-serial cable. After determining the connection method, you need to prepare materials such as AB PLC and corresponding programming software (such as RSLogix 5000), computer serial cable or USB-to-serial cable, and adapter (if you need to convert the 9-pin serial interface to 25-pin).
In terms of programming software selection, different AB PLC series may require different programming software. For example, RSLogix 500 is widely used for programming MicroLogix series and SLC 500 series PLCs; RSLogix 5000 is mainly for ControlLogix and CompactLogix series PLCs; Studio 5000 Logix Designer is a new generation software environment launched by Rockwell Automation, integrating multiple functions and providing more advanced features.

1.2. Configure network connection

When programming Allen Bradley PLC, configuring network connection is a key step. The first step is to assign IP address. AB PLC can choose static IP address assignment or dynamic IP address assignment. Static IP address allocation is suitable for situations where the network environment is stable, the number of devices is small and does not change frequently. It is necessary to determine the network interface and subnet mask of the device, select an unused IP address, and configure the device's IP address, subnet mask, gateway, DNS and other network parameters. Dynamic IP address allocation is suitable for situations where there are a large number of devices and the network environment changes frequently. IP addresses are automatically allocated through DHCP (Dynamic Host Configuration Protocol). The advantage is that it can easily manage a large number of devices and reduce the workload of manual configuration.
In terms of driver configuration, taking the computer connected to the PLC via a USB cable as an example, it is necessary to allocate an IP address and configure the driver. After opening the programming software, perform a communication test. After the local communication test is OK, change the gateway LAN port IP to the same network segment as the PLC, add this device in the comprehensive management background, and open the client software to build a channel to enable remote communication. HINET Industrial Intelligent Gateway is an equipment communication terminal product for the industrial field that integrates multiple Internet communication technologies. It supports multiple Internet access methods such as 4G, WIFI, Ethernet, etc., and can realize functions such as remote control of industrial field equipment and remote upgrade of equipment firmware.

2. Basic programming steps

2.1. Registration request and response

The format of the registration request is “65 00 04 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 The format of registration reply is “65 00 04 00 57 01 56 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00”. Registration request and response are the first step in establishing communication with Allen Bradley PLC, laying the foundation for subsequent operations.

2.2. Open Request and Response

  1. Standard Open Request: The format is “6f 00 40 00 57 01 56 00 00 00 00 00 8d 0c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 b2 00 30 00 54 " 02 20 06 24 01 05 f7 02 00 00 80 01 00 fe 80 02 00 1b 05 c0 80 a7 02 02 00 00 00 80 84 1e 00 f4 43 80 84 1e 00 f4 43 a3 03 01 00 20 02 24 01". In the standard open request, the size of the data service request packet is set to 500 bytes.
  1. Extended Open Request: The format is "6f 00 44 00 57 01 31 00 00 00 00 00 41 0d 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 b2 00 34 00 5b 02 20 06 24 01 05 f7 02 00 00 80 01 00 fe 80 02 00 1b 05 c0 80 a7 02 02 00 00 00 80 84 1e 00 a0 0f 00 42 80 84 1e 00 a0 0f 00 42 a3 03 01 00 20 02 24 01". The data service request data packet size range of the extended open request setting is 500~4000 bytes.
  1. Response format: The response formats of the standard open request and the extended open request are basically the same. For example, the format of the standard open response is "6f 00 2e 00 57 01 56 00 00 00 00 00 8e 0c 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 b2 00 1e 00 d4 00 00 00 4d 7c 9c ff 02 00 fe 80 03 00 1b 05 c0 80 a7 02 80 84 1e 00 80 84 1e 00 00 00”.

2.3. Read data request and response

The format of the read data request is “70 00 5c 00 57 01 56 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 a1 00 04 00 4d 7c 9c ff b1 00 48 00 8f 0c 0a 02 20 02 24 3 4c 45 50 55 4d 50 31 01 00 00 00 00 00". When reading tags and attributes, the tag name is usually used. The tag name is entered in the request, and the PLC returns the data corresponding to the tag to the host software according to the tag name. The properties can be unread, such as reading the properties and tags "PC_REALDATA_S0_INT.S0_PLC_HOUR". The format of the read data response is “70 00 3b 00 57 01 56 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 a1 00 04 00 02 00 fe 80 b1 00 27 00 8f 0c 8a 00 00 00 02 00 06 00 1a 00 83 00 00 00 02 00 01 00 00 00 00 00 03 00 00 00 2e 97 ba b8 d2 00 00 00 c1 00 00".

2.4. Write data request and response

The format of write data request is “70 00 3E 00 E8 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 A1 00 04 00 48 7C 9C FF B1 00 2A 00 D1 15 8A 00 00 00 03 00 08 00 1C 00 20 00 83 00 00 00 02 00 01 00 00 00 00 0003 00 00 00 2E 97 BA B8 D3 00 00 00 D3 00 00 00". In the write data request, the first layer command uses the 0x70 command and the 0x0a multi-data packet command, but it is different in each data service request packet. The command for reading data is 0x52 and the command for writing data is 0x53. The method for writing tags is to write the tag name in the request, such as writing the tag name "PC_PID_S0.S0_PID_VALVEAVERAGETEMP_D,PC_PID_S0.S0_PID_VALVEAVERAGETEMP_D1". The format of the write data response corresponds to the write data request.

2.5. Close request

3. Digital Conversion Function

3.1. Function Overview

The digital conversion function plays a vital role in Allen Bradley PLC (AB PLC). It allows analog signals such as temperature, pressure, flow, etc. to be converted into digital data for computer processing and analysis. AB PLC achieves this function through a built-in analog to digital converter (ADC).
In the field of industrial automation, analog signals are usually generated by sensors, but computers and controllers can usually only process digital signals. Therefore, the digital conversion function has become a key link between sensors and controllers. It can convert continuous analog signals into discrete digital signals, allowing PLCs to accurately read and process these signals, thereby achieving precise control of industrial processes.

3.2. Implementation steps

  1. Configure the input module to receive analog signals:
    • First, you need to select the appropriate input module according to actual needs. AB PLC provides a variety of input modules, including analog input modules and thermocouple input modules.
    • Determine the module slot number and input type. For example, assume that the module slot number used is 1 and the input type is thermocouple.
    • Connect the analog signal source to the input module and ensure that the connection is correct and reliable.
  1. Set the sampling rate and conversion accuracy:
    • The sampling rate determines the frequency at which the signal is sampled. A high sampling rate ensures a fast response to signal changes, which is essential for dynamic systems. Generally speaking, the sampling rate can be set according to the dynamic characteristics of the system and the requirements for response speed.
    • The conversion accuracy determines the accuracy of the converted signal. High resolution ensures that more signal details are captured, which is especially important in applications that require high-precision control. AB PLC usually provides different resolution options, which can be selected according to actual needs.
    • In addition, technical processing such as signal amplification, filtering and linearization should also be considered to ensure that the converted digital signal can accurately represent the original analog signal.
  1. Write program code to process the converted digital signal:
    • The following is a simple AB PLC programming example, showing how to write a program to achieve digital conversion through RSLogix 5000 software:
// Assume that the program is Allen-Bradley ControlLogix system
// Set analog input module
// Assume that the module slot number is 1 and the input type is thermocouple
// Read analog input value
N7:0 = * Analog Input [I:1.0]
// Convert the read analog signal value to temperature
// Assume that the value to be converted is stored in N7:0 and the converted temperature is stored in D1:0
// Call the function block for conversion, for example, use Allen-Bradley's dedicated function block
// The following is an example of a function block call
// BTU_TO_TEMP() is a hypothetical function block used to convert BTU units to degrees Celsius
BTU_TO_TEMP(N7:0, D1:0);
// The value in D1:0 can be used for further processing or control.

3.3. Case Analysis

Take temperature control as an example to show the process and importance of digital conversion in practical applications.
In actual industrial automation applications, AB PLC plays the role of control center. Taking temperature control on a production line as an example, the analog signal generated by the temperature sensor needs to be converted into a digital signal so that the AB PLC can process and control it.
First, the analog signal of the temperature sensor is processed by the signal conversion module and converted into a digital signal. In this process, it is necessary to select a suitable signal conversion module and configure it correctly according to the type of sensor and the range of the output signal.
Then, the AB PLC receives these digital signals and adjusts the cooling system to maintain the set temperature range according to the preset control logic. For example, the PID control algorithm can be used to calculate the output value of the cooling system that needs to be adjusted based on the difference between the current temperature and the set temperature.
The importance of digital conversion in temperature control is reflected in the following aspects:
  1. Improve the accuracy and stability of the system: Digital signal processing has high anti-interference ability, which can reduce the impact of electrical interference on temperature measurement and improve the accuracy and stability of the system.
  1. Easy to process and analyze data: Digital signals can be easily stored, transmitted and processed, which provides convenience for subsequent data analysis and optimization.
  1. Realize remote monitoring and control: Through network communication technology, digital signals can be transmitted to the remote monitoring center to achieve remote monitoring and control of temperature.
In short, the digital conversion function plays an important role in AB PLC programming. By correctly configuring the input module, setting the sampling rate and conversion accuracy, and writing appropriate program codes, accurate conversion and processing of analog signals can be achieved, providing strong support for industrial automation control.

4. Summary of programming methods

4.1. Key points

  1. In-depth understanding of programming equipment and software: Choose a suitable programming device such as a computer, and choose the corresponding programming software according to different AB PLC series, such as RSLogix 5000, Studio 5000 Logix Designer, etc. Be familiar with the device connection methods, including serial port connection and USB connection, and ensure the correct configuration of drivers and network connections.
  1. Master the communication protocol: Understand the format and process of communication protocols such as registration request and response, open request and response, read data request and response, write data request and response, and close request. These protocols are the basis for data exchange and control with AB PLC.
  1. Digital conversion function: Clarify the importance of digital conversion function in industrial automation, master the method of configuring input modules to receive analog signals, setting sampling rate and conversion accuracy, and writing program code to process converted digital signals.
  1. Modular programming: Using modular programming methods, the program is decomposed into independent, single-function modules to improve the readability and maintainability of the code. Each module performs a specific task and can be independently tested and verified.

4.2. Notes

  1. Follow industrial standards: AB PLC programming should follow international standards, such as IEC 61131-3, to ensure the consistency, maintainability and portability of the program. Programming should be logically clear and consistent, so that others can understand and maintain it.
  1. Write clear comments: Add detailed comments to the code, which are clear, concise, and relevant, and can clearly explain the function and role of the code segment. This is very helpful for programmers who may maintain or debug the program later.
  1. Avoid double coil output: In programming, pay attention to avoid using the coil of the same component twice or more in the same program, that is, double coil output. Double coil output may cause the program to run abnormally, and the program design should be optimized to avoid this situation.
  1. Consider program efficiency: When writing PLC programs, you should try to consider program efficiency and avoid using redundant code or excessive calculation operations to reduce the system's response time and resource usage.
  1. Perform rigorous testing and verification: After PLC programming is completed, rigorous testing should be performed to verify the function, including comprehensive testing of different situations and inputs, checking whether the output meets expectations, and making necessary adjustments and optimizations. At the same time, an error handling mechanism should be built in to ensure that the system can be safely handled in the event of an unexpected situation.
  1. Pay attention to safety issues: AB PLC system plays a key role in industrial control, so special attention should be paid to safety issues when programming. The safety of the system should be fully considered, and necessary measures should be taken to protect the safety of equipment and workers and avoid potential dangers and failures.
In short, AB PLC programming requires comprehensive consideration of all aspects, mastering key points, and paying attention to avoiding common problems in order to write high-quality and reliable programs to provide strong support for industrial automation control.