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How to Connect Micro 1400 PLC to HMI using RS232 Communication: Feasibility and Setup Advice

Question:

I am unsure if it is feasible, but I am looking to connect my Micro 1400 PLC to an HMI using RS232 communication and a RS232/TTL converter. The HMI is programmed in C++. Can anyone advise if this setup is possible or am I going in circles?

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When working with Allen-Bradley register-oriented PLCs, it's important to note that many of them use a protocol based on 'DF1'. This protocol dates back to the PLC-5 era and is still used in newer PLC implementations. The protocol has evolved over time, with variations found in PLC-5 and SLC-500 families. Some of the protocols based on DF1 include Data Highway, PLC-5 port 2222 Ethernet, and PCCC, which is compatible with CompactLogix. Recent advancements in protocol include type encodings for newer data types like 32-bit integers and character strings. For those looking to learn more about DF1, Publication 1770-6.5.16 from November 1991 is a great resource. This printed book offers valuable information in a user-friendly format. While some details on putting DF1 packets into Ethernet packets may not be readily available from Allen Bradley, the PCCC information is accessible. If you're seeking C-code communication libraries for serial DF1, they can be found online. However, some individuals prefer to learn through trial and error over the years. Feel free to reach out if you'd like to discuss Raspberry PI possibilities.

Utilizing Modbus is an alternative option to consider for communication. The HMI will need to actively retrieve data through polling, which could potentially impact performance. However, there is a wide availability of Modbus libraries in various programming languages that can be easily integrated.

Your project manager (PM) has indicated the use of multiple devices. When working with multiple devices in a serial setup, it is recommended to switch to RS-422 or RS-485. Typically, a '2-wire' RS-485 setup requires an isolated converter. Despite being labeled as 2-wire, it is important to remember the presence of a third wire. Serial communication with multiple devices involves sending out communication requests one at a time from the computer. The system then waits for each request to be completed either by receiving a reply from the Programmable Logic Controller (PLC) or a timeout before proceeding to the next request. It is not possible to simultaneously communicate with multiple PLCs or execute multiple requests to the same PLC in this setup. The speed of serial communication is often associated with baud rate, but other factors like half versus full duplex, packet size, and more also play a role in determining performance. In legitimate PLC protocols like Modbus, a one-byte identifier in the packet specifies which PLC should respond to the request. Each PLC connected in a multidrop setup must have a unique value assigned to this identifier. The DF1 protocol follows a similar approach. When serial protocols such as Modbus or DF1 are integrated into Ethernet systems, the one-byte identifier is retained. In some instances, this identifier may be disregarded as Ethernet routing relies on IP addresses for communication. However, in other scenarios, the identifier is utilized for protocol gateways.

The latest version of Studio5000, Ver 36, released around Thanksgiving, now features OPC UA integration. This update may offer a potential solution to your needs. Best regards.

@DustyC, are you inquiring about establishing connectivity between an HMI programmed in C++ or C# and an ML1400 PLC via serial RS232? Have you heard of AdvancedHMI Software, a solution designed to monitor and control PLC data efficiently? AdvancedHMI Software offers a range of features, including hardware compatibility, .NET software, HMI software, SCADA, PLC integration, Visual Studio support, and training resources. This versatile software is free to download and supports various AB PLCs, including the ML1400, with programming capabilities in MS .Net. Additionally, there are driver libraries available for purchase, like NET.ABLINK, which provides Allen-Bradley MicroLogix, SLC, and PLC-5 drivers for Visual Studio .NET and web development. These drivers make it simple to develop HMI .NET applications for different frameworks. When utilizing multiple devices on serial connections, it may be necessary to switch to RS-422 or RS-485, particularly '2-wire' 485 using an ISOLATED converter. Keep in mind that despite being called 2-wire, a third wire may also be involved. For serial communication between one 'master' and multiple 'slaves', the protocol used is Df1 half-duplex. It is crucial to determine if the aforementioned software products support this mode.

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Frequently Asked Questions (FAQ)

FAQ: FAQs:

Answer: 1. Can I connect a Micro 1400 PLC to an HMI using RS232 communication and a RS232/TTL converter? - Yes, it is possible to connect a Micro 1400 PLC to an HMI using RS232 communication and a RS232/TTL converter. 2. Is it feasible to establish communication between a Micro 1400 PLC and an HMI programmed in C++? - Yes, it is feasible to establish communication between a Micro 1400 PLC and an HMI programmed in C++ using RS232 communication. 3. What advice can you provide for setting up the communication between a Micro 1400 PLC and an HMI using RS232? - Ensure the RS232/TTL converter is properly configured, establish the communication protocol, and ensure compatibility between the devices and programming languages.

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