Using Ethernet

The default socket configuration enables you to implement these communication options as shown below.

Note that the Vision700 comprises a built-in Ethernet port that offers 8 sockets, as explained in the topic Vision700 - Using Ethernet.

MODBUS

PLC networks, PLC to PLC

Any controller within the network can be both master and slave. In order to be read by the master, a slave's application must contain the MODBUS IP Scan FB.

Using UDP to implement controller-to-controller communication

In order to communicate via Ethernet throughout your controller network, you must include an Ethernet Card Init FB in the ladder application of each networked controller. Remember, when using UDP, do not use the Socket: Connect or Socket: Close elements; these are only required by TCP applications.

Master

The master PLC Ladder application must include the elements shown below.

Step 1: Initializing the Ethernet card and configuring MODBUS

The MODBUS Configuration is linked to Socket 0, which is by default set to UDP.

Note ♦

A PLC defined as a UDP master can communicate with a number of slave devices.

Step 2: Using MODBUS Commands

Note ♦

Note that the operand addresses in slave PLCs are indirect addresses (pointers). In the figure below,the Slave: Start of Vector parameter is 15. This means that the master will begin reading from MI 15 in the slave PLC. Since the Read: Vector Length parameter is 3, the function takes the values in MI 15, 16 and 17.

The Master: Start of Vector parameter is 17; therefore the values will be written into MI 17, 18, and 19 in the master device.

Slave

The slave PLC Ladder application must include the elements shown below.

Step 1: Initializing the Ethernet card and configuring MODBUS

Step 2: Scan

To enable the master PLC to access the slave, include a MODBUS Scan FB in the slave's application.

Using TCP to implement controller-to-controller communication

In order to communicate via Ethernet throughout your controller network, you must include an Ethernet Card Init FB in the ladder application of each networked controller. When using TCP, you must use the Socket: Connect or Socket: Close element.

Master

The master PLC Ladder application must include the elements shown below.

Step 1: Initializing the Ethernet card, Socket, and Configuring MODBUS

In the figure below, the socket is configured to use TCP.

Step 2: Establishing the Ethernet Connection: Connect Socket

Note ♦

It is recommended that there be a time elapse of a few seconds after the Ethernet Card Initialization and before activating Socket Connect. A timer may be used for this purpose.

Step 3: Using MODBUS Commands

Note ♦

Note that the operand addresses in slave PLCs are indirect addresses (pointers). In the figure below, the Slave: Start of Vector parameter is 15. This means that the master will begin reading from MI 15 in the slave PLC. Since the Read: Vector Length parameter is 3, the function takes the values in MI 15, 16 and 17.

The Master: Start of Vector parameter is 17; therefore the values will be written into MI 17, 18, and 19 in the master device.

Step 4: Terminating the Ethernet connection: Close Socket

When you terminate the connection, use the 'Function in Progress' MB to ensure that you do not terminate the connection while data is being communicated.

Slave

The slave PLC Ladder application must include the elements shown below.

Step 1: Initializing the Ethernet card, Socket, and Configuring MODBUS

In the figure below, the socket is configured to use TCP.

Step 2: Scan

To enable the master PLC to access the slave, include a MODBUS Scan FB in the slave's application.

PC to PLC: Accessing PLC via SCADA

To enable the SCADA application to access the PLC, the PLC is defined as a slave device. The slave PLC Ladder application must include the elements shown below.

Step 1: Initializing the Ethernet card and configuring MODBUS

Port 502 is the well-known port for MODBUS applications.

Step 2: Scan

To enable the SCADA application to access the slave, include a MODBUS Scan FB in the slave's application.

Using Ethernet

Default Socket Configuration

MODBUS

PLC networks, PLC to PLC

Using UDP to implement controller-to-controller communication

Master

Slave

Using TCP to implement controller-to-controller communication

Master

Slave

PC to PLC: Accessing PLC via SCADA