PLC TCP Connection Setup

Overview

This lecture explains how to establish a TCP connection between two PLCs using the TCON (transmission connection) block, focusing on setting up the connection without transferring data.

Introduction to PLC Communication

• PLCs (Programmable Logic Controllers) can connect to other devices using network protocols like TCP, ISO, or UDP.
• Open user communication lets PLCs connect to non-Siemens devices (e.g., PCs, printers, servers).

Setting Up the TCON Block

• Use the TCON block to establish the communication connection between devices.
• Each connection requires an instance data block to store the connection parameters.
• The parameterization window configures connection parameters (partner type, IP address, connection type, etc.).
• Possible partner types: broadcast (all devices on network), multicast (specific group), or unspecified/single partner (with given address).
• Each new connection needs a unique data block containing remote address, port, and other info.

Connection Configuration Steps

• Set remote IP address and select connection type (typically TCP for stability).
• Assign a unique connection ID to each connection for later data transfers.
• Choose active or passive connection establishment: one PLC must be active, the other passive.
• Specify local port only for the passive (not active) partner; active partner selects a free port automatically.

Understanding Ports

• Ports are logical communication endpoints, similar to gates at an airport.
• Only the passive PLC needs a designated open port (e.g., port 2000) for the connection.
• Active PLC sends data to the passive partner's open port; port selection on active side is optional.

Testing and Monitoring the Connection

• Use a memory bit (e.g., "connect") as a trigger to attempt connection on each PLC.
• The passive PLC should open its port and wait for the active PLC to connect.
• Status codes (e.g., 7002 = waiting, 7000 = no job) indicate connection states and help with troubleshooting.
• Set a "connected" memory bit when the connection is successfully established for easy monitoring.
• Use memory reset (MRES) to clear connection data during testing.

Key Terms & Definitions

• PLC (Programmable Logic Controller) — a digital computer used for automation of electromechanical processes.
• TCON block — a communication block to establish network connections between devices.
• Instance data block — storage for function block parameters and data, unique per connection.
• TCP (Transmission Control Protocol) — a reliable, stable network protocol for data transmission.
• Port — a logical endpoint for network communication on a device.
• Passive/Active Partner — passive opens a port and waits; active initiates the connection.

Action Items / Next Steps

• Practice configuring TCON blocks on two PLCs and assign correct roles (active/passive).
• Set up and test memory bit triggers to confirm the connection establishment.
• Review status/error codes for troubleshooting connection issues.
• Prepare for the next lesson, which will cover exchanging data after connection is established.