Citect Scada and Melsec-F protocol

[jerrycat]

I have been working on a multidrop network between 7 FX serie PLC. the Purpose of the network is to collect data from and monitor the PLC using Citect Scada. i know that the FX serie PLC support multidrop networking. (Mitsubishi sell the these modules ).. in the manual of citect is written the the melsec - F protocol which the FX -serie uses doesn't support multidrop networking. Will i be able to communicate with the 7 PLC using Citect scada using only one Com port on the PC

[dajcarj]

Maybe it could help similar application. We use a driver FX485ADP from Beijers (e-terminals) to create RS485 network with an E-terminal and 5FXs. E-terminal acts like master and collects datas from FX slaves (max 8). The driver uses Protocol Format 1 with checksum control for the communication with the PLC system. Jiri

[waynes]

Hi jerrycat, The guys at my company also use Citect/ MX4 to communicate to FX (FX2N©/FX0N/FX1N) plc's. As far as I have gathered, the protocol driver is not written to support multiple PLC on a singular network. If you could get the guys from Citect to change the code, then it would solve your problem. However, that may take time, if they agree to do it. You only other option is to use RS422 cards in your central PC. Or, alternatively, you could pop these plc's onto a ethernet network and monitor them that way. I generaly use the cards available from Moxa (http://www.moxa.com. They seem to do the job well. For the ethernet to RS422 conversion side, I use the DE311. The com ports are mapped as local ports on the pc using the supplied drivers. Hope this helps

[jerrycat]

waynes, the PC that i am planning has an RS485/422 card from advantech. the card has only dual ports. i planning to use 0ne to port to communicated with 7 PLC's of omron that are in a hostlink network. this is not the problem, Citect clearly stated in the user guide that is possible. the other port i will use to communicate with the 7 FX PLC that are in an multidrop network. Will i be able to communicate with the 7 PLC using only one port and different station adresses for the PLC. Why does citect said the FX2n protocol is a point to point sulotion and that it does not support multidrop network.

[waynes]

jerrycat, I remember once when I was analysing the protocol. The protocol in itself does not allow you to address multiple nodes. The conversation starts with: Host: 05 PLC: 06 This is where I think the problem starts. The host send an 0x05 (ENQ) and gets an ACK (0x06) back. When more than one of these PLC's are connected, you will get multiple ACK's back. I have found no other way to do this. (One master, multiple slaves). The use of mini-net may be an answer, but I am not sure how many nodes you can attach to this network. Does anybody else know of a solution.

[Jimbo]

Hello, I have an operational multidrop network between 11 FX PLC's and citect. i think we used a FX485 module but i am not exactly sure of the type. i ll look it up at work. Jimbo

[jerrycat]

Hi JimBo, you are probably using the FX-485 -ADP module or the FX-485-BD. How many serial ports are you using to communicate with the 11 PLC's?

[Jimbo]

Hey, Indeed thats the module FX485-ADP. I used just one serial port, and i readout about 25 words of every PLC. The speed is not super fast but any change of state is reported within 500 ms i think. this is more than fast enough for the application, is a monitoring station for a tunnel. Jimbo

[jerrycat]

It helps a lot to know that someone as a working apllication. i didn,t want lay down the fysical network to find out that i had to look for a other sulotion . many thanks