Send TCP/IP message from PLC to PC using Ladder Program

Question

Consider the following Ladder Program that checks if a connection is enabled (A202.00) then send a message from the PLC to the PC.

The documentation (Omron CX-Programmer) has a severe lack of explanation of the program convention. What I do not understand is:

1. To send a message from a node to a node. I should need to specify the receiver ID. It seems the function block does not have an option where I can insert an IP address. Am I supposed to MOV an IP address to a DM address (D300) then use it? If that's the case how (IP address has dots in between 4 bytes..)?

2. Can someone please explain what is S (First source word), D (First destination word) and C (First control word). Aren't they just memory address? E.g. sending content of a memory adress to another memory address?

[EDIT]

What am I trying to do?

I am trying to interface a measuring gauge (controlled through Ethernet by PC/C# application) to a robotic system (no RS232 or serial, no TCP/IP, only has the simplest I/O points) with an Omron PLC. When gauge completes a measurement, the C# app sends a command to the Omron PLC which, according to the command received, switch ON or OFF an output which triggers a voltage flow to the robot's I/O port.

Should I use FINS? What functions/protocol from the PLC I need to know to do this? I do not know so I am testing every function from the documentation. So far, zero progress.

Answer 1

1) All addressing information is encapsulated in the five control words (C -> C+4). C- "First Control Word" is the pointer to the first word in this table of five words you must have stored somewhere in your PLC to set up the communication.

2) First source word points to the first word in your PLC you wish to send. First destination word points to the first address in the PLC/device you wish to send to. In the example , the first control word specifies that 10 words should be sent. You point to the first one and it will send that one plus the next nine addresses as well.

To do this you have to use FINS communication - the PC stores a memory structure similar to the PLCs (CIO, DM, etc) called Event Memory and these are the addresses in the PC you are pointing to. The PC gets a FINS node number and address just like a PLC would - no IP addresses are involved. (see : FINS Manual) FINS is old, however, and has been superceded by things like Sysmac Gateway.

There are much better ways of communicating between PLC/PC, however, depending on what you are trying to do. Are you trying to write an HMI? If so, what language are you using?

Edit :

If you're using C#, I highly recommend you look into Sysmac Gateway and CX-Compolet. This is probably the most flexible, simple, and extensible way to get .NET working with Omron PLCs. If it is at all possible, however, a better way might even be to have the measurement unit communicate directly with the PLC via hardware I/O (relays, DIO, etc).

CX-Compolet, Sysmac Gateway link:

http://www.ia.omron.com/product/family/63/index_l_u.html