RBE/ECOM100 PC-PLC Communications

[johnr]

Using the RBE configuration and protocols, is it possible to send host PC-Initiated messages and have them read by RBE-formatted RX instructions in the PLC, when the RX is not simply reading a response to the previous WX?

I've successfully implemented the RBE example (both message and response back).  I've tried formatting a non-response PC message to be read by the PLC, and I think I'm close, but not quite there. 

My PC-Initiated host message:
48 41 50 2A 00 00 00 09 00 00 00 00 00 54 65 73 74 3F

The automatic response from an H0-ECOM100 (all WX/RX ladder code rungs turned off):
48 41 50 2A 00 00 00 04 00 00 00 00 00

But, when I activate the RX rung doing periodic reads, the RX instruction doesn't ever place my test message in the indicated buffer, as it does when the PLC reads a WX response message.  Is it possible to make this work at all?  Do I need to implement CRC when initiating a message, and/or are there any other critical header bytes (after the message length bytes) that need to be set a certain way?  Any help or pointing me to the proper documents would be appreciated.

I realize that I can use the SDK DLL to initiate a message, but for the application I have in mind I like the idea of using the RBE setup with simple UDP datagrams.  I would simply prefer that the PC could also be the initiator of communications.  Thanks.

[Greg]

The purpose of the RBE design was so the ECOM100 could initiate communications to a PC, since that was the unusual case. If you want the PC to initiate the communications, then, yes, you should use the Ethernet SDK, or Modbus TCP. With either of these it is not even necessary to program any ladders at all (i.e. no ladder overhead). The Ethernet SDK just writes to V-memory without there having to be an RX in the ladders at all. Same for Modbus TCP.

So, rather than trying to use the RBE (which was desiged to go from ECOM100 --> PC) you should use one of the other 2 (which were designed to go from PC --> ECOM100).

[johnr]

Dang, I was afraid that would be the answer.  Seems like it all must be there, given the built-in ECOM response...  Driver-less communication, needing only TCP/UDP sockets connection allows for a lot of flexibility in implementation.  Thanks for the reply.

[Greg]

The problem is that in the RBE, data is sent back in the ACK coming from the PC. It is not possible just to initiate an ACK with data from the PC. Thus, for data from the PC to get back to the ECOM100, it has to come in an ACK from the PC, and that would only happen if the ECOM100 sent a telegram to start with.