Explicit Messaging

Overview

uses the and /IP protocols to implement both and messaging.

This chapter explains the 140 NOC 78• 00 head module and its use of explicit messaging for request-and-reply communications for non-real-time information (like configuration and diagnostic data). A network node that receives a TCP/IP-encapsulated explicit message processes the message and generates a response.

NOTE:

The 140 NOC 78• 00 head module can process 16 MBP_MSTR blocks per MAST cycle.
The 140 NOC 78• 00 head module processes MBP_MSTR blocks to reach data on the control network only.

NOTE: If you receive a detected error message — stating that the 140CRP31200 module does not have a link (has no cable), MSTR functionality may not be available. If this happens, check that your cables are connected properly.

This chapter describes how to use both Control Expert function block logic and the Control Expert interface to send explicit messages.

What Is in This Chapter?

This chapter contains the following sections:

EtherNet/IP™

A network communication protocol for industrial automation applications that combines the standard internet transmission protocols of TCP/IP and UDP with the application layer common industrial protocol (CIP) to support both high speed data exchange and industrial control. EtherNet/IP employs electronic data sheets (EDS) to classify each network device and its functionality.

TCP/IP

Also known as internet protocol suite, TCP/IP is a collection of protocols used to conduct transactions on a network. The suite takes its name from 2 commonly used protocols: transmission control protocol and internet protocol. TCP/IP is a connection-oriented protocol that is used by Modbus TCP and EtherNet/IP for explicit messaging.

UDP

(user datagram protocol) A transport layer protocol that supports connectionless communications. Applications running on networked nodes can use UDP to send datagrams to one another. UDP does not always deliver datagrams as reliable or ordered as those delivered by TCP. However, by avoiding the overhead required for TCP, UDP is faster. UDP may be the preferred protocol for time-sensitive applications, where dropped datagrams are preferable to delayed datagrams. UDP is the primary transport for implicit messaging in EtherNet/IP.

explicit messaging

TCP/IP-based messaging for Modbus TCP and EtherNet/IP. It is used for point-to-point, client/server messages that include both data (typically unscheduled information between a client and a server) and routing information. In EtherNet/IP, explicit messaging is considered class 3 type messaging, and can be connection-based or connectionless.

implicit messaging

UDP/IP-based class 1 connected messaging for EtherNet/IP. Implicit messaging maintains an open connection for the scheduled transfer of control data between a producer and consumer. Because an open connection is maintained, each message contains primarily data, without the overhead of object information, and a connection identifier.

MAST

A master processor task that is run through its programming software. The MAST task has 2 sections:

IN: Inputs are copied to the IN section before execution of the MAST task.
OUT: Outputs are copied to the OUT section after execution of the MAST task.