Modbus between RX3i CPE 305 and Energymeter

[saineshkumar190]

Sir,
I'm new to modbus and getting help from GFK 2439 for RTU modbus between CPE305(PORT - 1) and Energymeter. But i'm getting an error of 304h (SHORT_RSP_ERROR that describes Incomplete response detected, response discarded.). What does this means and what is the solution. Can anyone help please.

 

[Steve Bailey]

GFK2439 is the manual for the Ethernet network interface unit. Nothing in that manual applies to serial communications through port 1 of the CPU module.

 

[saineshkumar190]

Sir,
Thanks for your reply. But as i've googled and found that CPE 305 doesn't support commreq. So, as suggested by my colleague i'm using this as in this Local User Logic in the Ethernet NIU can call a “C” block (built into the Ethernet NIU)to do Modbus communication.

 

[Steve Bailey]

You need to clarify your terminology. Generally, when people use the term "Modbus RTU" they are talking about using the Modbus protocol over an RS23 or RS485 serial cable, not a cat 5 or cat 6 Ethernet cable. When you use the Modbus protocol over Ethernet media, that is called Modbus TCP/IP.

Port 1 on an RX3I CPUE05 is a serial port. It can not be a Modbus RTU master. To use it for communications with your energy meter, the meter will have to be a Modbus RTU master and the PLC port 1 configured as a Modbus RTU slave.

You can use the Ethernet port on the CPE305 for Modbus TCP/IP. For that to work, your energy meter will have to be capable of Ethernet communications. Is that the case?

 

[RussB]

You can use the Ethernet port on the CPE305 for Modbus TCP/IP. For that to work, your energy meter will have to be capable of Ethernet communications. Is that the case?

Another possibility here could be a Modbus TCP/IP to RTU gateway.

 

[saineshkumar190]

Sir,
Sorry for wrong Terminology. Energymeter is configured as Modbus RTU.

I've configured my CPE305 Port - 1 (RJ-25) as Serial I/O. (Is it correct??)

Also i'm using Moxa TCC - 100 in between of PLC and Energymeter.

Ethernet port i cannot use because it is used for QuickPanel. So, i'm having only one port i.e. RJ - 25.

 

[Steve Bailey]

Use your Quick Panel's serial port to communicate with the energy meter.

 

[saineshkumar190]

Sir,
Thanks for ur support its communicating now.

 

[dovi]

If I connect a device which is Modbus RTU Master to CPE305 port 1 (config. to Modbus RTU Slave)- Do I need to insert logic for the comm. to take place ?

 

[tamir]

Hi Dovi,
I have CPE305 connected to PC with HMI by Modbus ETH and all we need is to set the configuration to Standards Modbus Addressing.
The master is the HMI program in PC.

 

[dovi]

You're using ETH but I need RTU

 

[Steve Bailey]

If I connect a device which is Modbus RTU Master to CPE305 port 1 (config. to Modbus RTU Slave)- Do I need to insert logic for the comm. to take place ?

No.

 

[dovi]

So the master read data from the PLC's data table mapped like at MBTCP - %M for bool , %R for holding registers etc. ?

 

[dovi]

I just got the RJ25-DB9 232 cable & checked online with Modscan - comm. is working without any logic. Thanks

 

[RussB]

So the master read data from the PLC's data table mapped like at MBTCP - %M for bool , %R for holding registers etc. ?

Yes