Connect Two PLCs in Minutes—Modbus P2P Made Simple
Connect two Do-More PLCs peer-to-peer over Modbus TCP using the Modbus Scanner — read and write 100 discrete bits and registers with no supervisory system.
⚡ QUICK ANSWER
Modbus is an open industrial protocol for exchanging data between devices, and the Do-More Designer software includes a Modbus I/O Scanner that makes linking two PLCs straightforward. This setup is peer-to-peer: the two controllers talk directly to each other on the same network, with no supervisory control system sitting in between — which means faster data exchange and a simpler overall architecture. One PLC acts as the Modbus server and the other as the client that initiates the reads and writes. Understanding Modbus addressing is the part that trips people up: coils and discrete inputs are single bits, holding and input registers are 16-bit words, and each is referenced by an address range, so you need to know which type you're reading and where it lands in your PLC's memory. Here the Do-More Designer Simulator PLC and a BRX Do-More PLC exchange 100 discrete bits and 100 registers in both directions over Modbus TCP, and the link is monitored and tested to confirm the data is moving. The full step-by-step is in the guide below.
📖 FULL WRITTEN TUTORIAL + DOWNLOADS (client & server programs)
https://accautomation.ca/do-more-plc-...
⏱️ TIMESTAMPS
0:00 - Introduction: P2P Modbus Scanner Communication
1:40 - What Is Modbus?
2:57 - What Are Modbus Addresses?
4:03 - Programming the Modbus Server PLC
7:16 - Programming the Modbus Client PLC
12:29 - Monitoring the P2P Modbus TCP Communication
13:32 - Testing the Network
📚 WHAT YOU'LL LEARN
✅ What Modbus is and how peer-to-peer communication works
✅ How Modbus addresses are structured — bits versus registers
✅ How to program the Modbus server PLC
✅ How to program the Modbus client PLC with the Modbus I/O Scanner
✅ How to monitor and test the link exchanging 100 bits and registers
❓ FREQUENTLY ASKED
Q: What is peer-to-peer Modbus communication?
A: Two devices communicating directly with each other on the same network, with no supervisory control system in between — which speeds up data exchange and simplifies the system architecture. The full setup is in the guide.
Q: What are Modbus addresses?
A: Modbus data is organised into types — coils and discrete inputs are single bits, holding and input registers are 16-bit words — and each type has its own address range, so you need to know which you're accessing and where it maps in the PLC.
Q: What's the difference between the Modbus client and server?
A: The client initiates the requests — the reads and writes — and the server responds to them. Here the Modbus I/O Scanner in Do-More Designer acts as the client side of the link.
👉 Full step-by-step: https://accautomation.ca/do-more-plc-...
🔗 MORE RESOURCES
🎮 Free ACC PLC Simulator (our own 3D-scene browser simulator, no install): https://accautomation.ca/simulator/
▶ BRX Do-More PLC Series: https://accautomation.ca/series/brx-d...
▶ Numbering Systems & Addressing: • BRX Controller Memory Allocation | Do-More...
▶ Modbus ASCII Protocol: • BRX Do-More PLC Modbus ASCII Protocol Now!
▶ PLC Beginners Guide: https://accautomation.ca/programming/...
▶ Free eBooks: https://accautomation.ca (subscribe for download)
🛒 RECOMMENDED HARDWARE
▶ Shop: https://www.automationdirect.com/
▶ Parts Guide: https://www.accautomation.ca/purchase...
💬 Questions? Drop a comment below.
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Regards,
Garry
ACC Automation
http://www.accautomation.ca