I really realy hate Modbus
Me too, but it is because no one implements Modbus RTU correctly.
I have always prefer Rockwell's DF1 because it isn't timing dependent and can be full duplex. The only down side of DF1 is that it is only a data link layer so there is no definition of what is in the packet.
and that is why I bought the DSPSX because I asked them if they could communicate with an FX and they said yes.
I bet it can if the Mitsubushi PLC can. So far you haven't established that the Mitsubishi PLC can use Modbus RTU. Back in the dark ages I would use a serial port data analyzer to monitor the data going back and forth. I would get to the bottom of the problem quickly. I could also use a scope to check for parities and start and stop bits.
I never use Modbus RTU though because at that time there were no Modbus RTU libraries or Mitsubishi serial cards for a FX2N. You do know that the
I guess one more company to cross of the list. This is from Red Lion tech supports last email
[FONT="]We have hundreds of protocols and unfortunately writing how to's for every plc companies release that use that protocol isn't something we've been able to keep up with. Sorry its been upsetting for you[/FONT]
I would side with Red Lion on this one. Are you claiming that Red Lion doesn't have a working Modbus RTU? If the Red Lion is sending out the correct data then it is the Mitsubishi's fault. I would blame Mitsubishi. It seems that Mitsubishi changes the protocol for every series of PLC.
So here is a question. Have your tried communicating between the DSPSX and a PC setup as a slave or master? There is plenty of free software out there for Modbus RTU. Have you done the same between a PC and the Mitsubishi?
One of our best distributors is in South Korea. They use Mitsubishi PLCs. I have had nothing but frustration getting Ethernet to work with Mitsubishi PLCs. Why am I doing it? Because our customers and distributors can't make it work but when they do work and they are fast.
I don't think you have gone about this correctly. I don't think the forum has asked the right questions.
You aren't the only one.
http://forums.mrplc.com/index.php?/topic/20120-fx3u-as-modbus-slave/