H4-ECOM100 Modbus Master Not Communicating

[jamesh]

Hi,

I have a DL450 PLC fitted with an ECOM100 card that is set up as a Modbus master.
I am using a Modbus simulator on my computer to act as the slave however I am not getting any requests from the PLC.
When I monitored the communication with wireshark it is picking up TCP packets from the ECOM but is not identifying them as Modbus.



The peer to peer settings are:


PLC Code:


Any help with this will be appreciated.

[Controls Guy]

I think you have to have another Ibox ahead of the ECWX in ladder to set up the module.  "ECOM100" I think?  There's also a dip switch or something to physically set on the ECOM100 as well IIRC.

[jamesh]

I have an ECOM100 box at the top of the ladder.
Dip switch 7 is apparently only required for advanced comms such as email, I switched it on anyway.

[Greg]

jamesh, according to the picture you posted, the ECOM100 is sending out TCP synchronization telegrams but not getting any reply from your PC?

Thus, the ECOM100 looks like it cannot establish a TCP connection with your PC.

[jamesh]

Thanks Greg,

It turns out it was a problem with my computer. Curiously the Modbus emulator I am using is able to act as a Client to the ECOM but not as a Server on my Windows 7 machine. I managed to get it to act as a Server on the Windows XP virtual machine. Another thing I noticed is when reading multiple coils the requests will only go to word offsets regardless of the setting of the Slave Element i.e. you can only read coil addresses starting at 1, 17, 31 etc.